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Filed Pursuant to Rule 497
Registration Statement Nos. 333-180689 and 333-180690

PROSPECTUS SUPPLEMENT

(to Prospectus dated July 10, 2012)

5,250,000 Shares

New Mountain Finance Corporation

Common Stock

New Mountain Finance Corporation (“NMFC”) is a holding company with no direct operations of its own, and its only business and sole asset is its ownership of common membership units of New Mountain Finance Holdings, L.L.C. (the “Operating Company”). The Operating Company is an externally managed business development company managed by New Mountain Finance Advisers BDC, L.L.C. and is the operating company for NMFC’s business. NMFC and the Operating Company each have elected to be treated as a business development company under the Investment Company Act of 1940. The Operating Company’s investment objective is to generate current income and capital appreciation through the sourcing and origination of debt securities at all levels of the capital structure, including first and second lien debt, notes, bonds and mezzanine securities. NMFC owns approximately 34.6% of the common membership units of the Operating Company and New Mountain Finance AIV Holdings Corporation owns approximately 65.4% of the common membership units of the Operating Company.

We are offering for sale 5,250,000 shares of NMFC’s common stock. We have granted the underwriters a 30-day option to purchase up to 787,500 additional shares of NMFC’s common stock at the public offering price, less the underwriting discounts and commissions.

NMFC’s common stock is listed on the New York Stock Exchange under the symbol “NMFC”. On July 10, 2012, the last reported sales price on the New York Stock Exchange for NMFC’s common stock was $14.78 per share.

An investment in NMFC’s common stock is very risky and highly speculative. Shares of closed-end investment companies, including business development companies, frequently trade at a discount to their net asset value. In addition, the companies in which NMFC invests, through the Operating Company, are subject to special risks. See “Risk Factors” beginning on page 19 of the accompanying prospectus to read about factors you should consider, including the risk of leverage, before investing in NMFC’s common stock.

This prospectus supplement and the accompanying prospectus contain important information about NMFC and the Operating Company that a prospective investor should know before investing in NMFC’s common stock. Please read this prospectus supplement and the accompanying prospectus before investing and keep it for future reference. NMFC and the Operating Company file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission (http://www.sec.gov), which is available free of charge by contacting NMFC by mail at 787 Seventh Avenue, 48th Floor, New York, New York 10019 or on our website at http://www.newmountainfinance.com. Information contained on our website is not incorporated by reference into this prospectus supplement and the accompanying prospectus, and you should not consider that information to be part of this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares against payment in New York, New York on or about July 17, 2012.

Joint-Lead Bookrunners

Co-Lead Managers

Co-Managers

A division of Scott & Stringfellow, LLC

Prospectus Supplement dated July 12, 2012.

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PROSPECTUS SUPPLEMENT

PROSPECTUS

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ABOUT THIS PROSPECTUS SUPPLEMENT

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus. Neither we nor the underwriters have authorized any other person to provide you with different information from that contained in this prospectus supplement or the accompanying prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to buy, any shares of our common stock by any person in any jurisdiction where it is unlawful for that person to make such an offer or solicitation or to any person in any jurisdiction to whom it is unlawful to make such an offer or solicitation. The information contained in this prospectus supplement and the accompanying prospectus is complete and accurate only as of their respective dates, regardless of the time of their delivery or sale of our common stock. This prospectus supplement supersedes the accompanying prospectus to the extent it contains information different from or additional to the information in that prospectus.

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering of common stock and also adds to and updates information contained in the accompanying prospectus. The second part is the accompanying prospectus, which gives more general information and disclosure. To the extent the information contained in this prospectus supplement differs from the information contained in the accompanying prospectus, the information in this prospectus supplement shall control. Please carefully read this prospectus supplement and the accompanying prospectus together with any exhibits and the additional information described under “Available Information” and in the “Summary” and “Risk Factors” sections before you make an investment decision.

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FEES AND EXPENSES

The following table is intended to assist you in understanding the costs and expenses that you will bear directly or indirectly. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus supplement and the accompanying prospectus contains a reference to fees or expenses paid by “you”, “NMFC”, the “Operating Company”, or “us” or that “we”, “NMFC”, or the “Operating Company” will pay fees or expenses, stockholders will indirectly bear such fees or expenses through NMFC’s investment in the Operating Company.

Example

The following example, required by the SEC, demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in NMFC’s common stock. In calculating the following expense amounts, we have assumed that our borrowings and annual operating expenses would remain at the levels set forth in the table above. See Note 6 below for additional information regarding certain assumptions regarding our level of leverage.

The example and the expenses in the tables above should not be considered a representation of future expenses, and actual expenses may be greater or less than those shown.

While the example assumes, as required by the applicable rules of the SEC, a 5.0% annual return, our performance will vary and may result in a return greater or less than 5.0%. The incentive fee under the Investment Management Agreement, which, assuming a 5.0% annual return, would either not be payable or would have an insignificant impact on the expense amounts shown above, is not included in the example. The above illustration assumes that we will not realize any capital gains (computed net of all realized capital losses and unrealized capital depreciation) in any of the indicated time periods. If we achieve sufficient returns on our investments, including through the realization of capital gains, to trigger an incentive fee of a material amount, our expenses and returns to our investors would be higher. For example, if we assumed that we received our 5.0% annual return completely in the form of net realized capital gains on our investments, computed net of all cumulative unrealized depreciation on our investments, the projected dollar amount of total cumulative expenses set forth in the above illustration would be as follows:

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The example assumes a sales load of 3.2%. In addition, while the examples assume reinvestment of all distributions at net asset value, participants in NMFC’s dividend reinvestment plan will receive a number of shares of NMFC’s common stock determined by dividing the total dollar amount of the distribution payable to a participant by the market price per share of NMFC’s common stock at the close of trading on the dividend payment date. The market price per share of NMFC’s common stock may be at, above or below net asset value. See “Dividend Reinvestment Plan” in the accompanying prospectus for additional information regarding the dividend reinvestment plan.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement contains forward-looking statements that involve substantial risks and uncertainties. These forward-looking statements are not historical facts, but rather are based on current expectations, estimates and projections about us, the Operating Company’s current and prospective portfolio investments, our industry, our beliefs, and our assumptions. Words such as “anticipates”, “expects”, “intends”, “plans”, “believes”, “seeks”, “estimates”, “would”, “should”, “targets”, “projects”, and variations of these words and similar expressions are intended to identify forward-looking statements. The forward-looking statements contained in this prospectus supplement involve risks and uncertainties, including statements as to:

These statements are not guarantees of future performance and are subject to risks, uncertainties, and other factors, some of which are beyond our control and difficult to predict and could cause actual results to differ materially from those expressed or forecasted in the forward-looking statements, including without limitation:

Although we believe that the assumptions on which these forward-looking statements are based are reasonable, any of those assumptions could prove to be inaccurate, and as a result, the forward-looking statements based on those assumptions also could be inaccurate. Important assumptions include the Operating

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Company’s ability to originate new loans and investments, certain margins and levels of profitability and the availability of additional capital. In light of these and other uncertainties, the inclusion of a projection or forward-looking statement in this prospectus supplement should not be regarded as a representation by us that our plans and objectives will be achieved. These risks and uncertainties include those described or identified in “Risk Factors” and elsewhere in this prospectus supplement and the accompanying prospectus. You should not place undue reliance on these forward-looking statements, which apply only as of the date of this prospectus supplement. However, we will update this prospectus supplement to reflect any material changes to the information contained herein. The forward-looking statements and projections contained in this prospectus supplement are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, as amended, or the Securities Act.

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CAPITALIZATION

The following table sets forth our capitalization as of March 31, 2012:

You should read this table together with “Use of Proceeds” and financial statements and related notes thereto included elsewhere in this prospectus supplement and the accompanying prospectus.

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USE OF PROCEEDS

The net proceeds from the sale of the 5,250,000 shares of NMFC’s common stock in this offering are estimated to be approximately $72.5 million after deducting estimated offering expenses of approximately $0.4 million payable by the Operating Company and underwriting discounts and commissions of approximately $2.4 million, which is net of the $0.6 million of commissions which the Investment Adviser has agreed to bear in connection with this offering. This amount will not be subject to reimbursement by either NMFC or the Operating Company.

The Operating Company intends to use the net proceeds from this offering for new investments in portfolio companies in accordance with the Operating Company’s investment objective and strategies described in this prospectus supplement and the accompanying prospectus, to temporarily repay indebtedness (which will be subject to reborrowing), to pay our operating expenses, to pay distributions to our stockholders/unit holders and for general corporate purposes. The Operating Company is continuously identifying, reviewing and, to the extent consistent with its investment objective, funding new investments. As a result, we typically raise capital as we deem appropriate to fund such new investments.

We estimate that it will take three to six months for the Operating Company to substantially invest the net proceeds of this offering, depending on the availability of attractive opportunities and market conditions. However, we can offer no assurance that we will be able to achieve this goal.

Proceeds not immediately used for new investments or the temporary repayment of debt will be invested primarily in cash, cash equivalents, U.S. government securities and other high-quality investments that mature in one year or less from the date of investment. These temporary investments are expected to provide a lower net return than we hope to achieve from the Operating Company’s target investments.

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UNDERWRITING

NMFC, the Operating Company and the underwriters named below have entered into an underwriting agreement with respect to the shares being offered. Subject to certain conditions, each underwriter has severally agreed to purchase the number of shares indicated in the following table. Goldman, Sachs & Co., Wells Fargo Securities, LLC and Morgan Stanley & Co. LLC are the representatives of the underwriters.

The underwriters are committed to take and pay for all of the shares being offered, if any are taken, other than the shares covered by the option described below unless and until this option is exercised.

If the underwriters sell more shares than the total number set forth in the table above, the underwriters have an option to buy up to an additional 787,500 shares from NMFC. They may exercise that option for 30 days. If any shares are purchased pursuant to this option, the underwriters will severally purchase shares in approximately the same proportion as set forth in the table above.

The following table shows the per share and total underwriting discounts and commissions (sales load) to be paid to the underwriters by the Operating Company. Such amounts are shown assuming both no exercise and full exercise of the underwriters’ option to purchase 787,500 additional shares. In addition, the Investment Adviser has agreed to bear an additional $577,500, or $0.11 per share, and $664,125, or $0.11 per share, respectively, of commissions (sales load) in connection with this offering in the event of no exercise and full exercise of the underwriters option to purchase 787,500 additional shares, which is not reflected in the following table.

Because the Financial Industry Regulatory Authority, or FINRA, views the common stock offered hereby as interests in a direct participation program, the offering is being made in compliance with the requirements of FINRA Rule 2310. In compliance with such requirements, the underwriting discounts and commissions in connection with the sale of securities will not exceed 10.0% of gross proceeds of this offering. Investor suitability with respect to the common stock should be judged similarly to suitability with respect to other securities that are listed for trading on a national securities exchange.

In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers and may at any time hold long and short positions in such securities and instruments. Such investment and securities activities may involve securities and instruments of the issuer. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

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Shares sold by the underwriters to the public will initially be offered at the public offering price set forth on the cover of this prospectus supplement. Any shares sold by the underwriters to securities dealers may be sold at a discount of up to $0.4640 per share from the public offering price. If all the shares are not sold at the initial offering price, the representatives may change the public offering price and the other selling terms. The offering of the shares by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part.

NMFC, each of its officers and directors, and each of the members of the Investment Adviser’s investment committee have agreed with the underwriters, subject to certain exceptions, not to dispose of or hedge any shares of NMFC’s common stock or securities convertible into or exchangeable for shares of NMFC’s common stock during the period from the date of this prospectus supplement continuing through the date 90 days after the date of this prospectus supplement, except with the prior written consent of Goldman, Sachs & Co., Wells Fargo Securities, LLC and Morgan Stanley & Co. LLC.

The 90 day restricted period described in the preceding paragraph will be automatically extended if: (1) during the last 17 days of the 90 day restricted period the NMFC issues an earnings release or announce material news or a material event; or (2) prior to the expiration of the 90 day restricted period, the NMFC announces that it will release earnings results during the 15-day period following the last day of the 90 day period, in which case the restrictions described in the preceding paragraph will continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release of the announcement of the material news or material event.

NMFC’s common stock is listed on the New York Stock Exchange under the symbol “NMFC”.

In connection with the offering, the underwriters may purchase and sell shares of common stock in the open market. These transactions may include short sales, stabilizing transactions and purchases to cover positions created by short sales. Short sales involve the sale by the underwriters of a greater number of shares than they are required to purchase in the offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares from us in the offering. The underwriters may close out any covered short position by either exercising their option to purchase additional shares or purchasing shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase additional shares pursuant to the option granted to them. “Naked” short sales are any sales in excess of such option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the common stock in the open market after pricing that could adversely affect investors who purchase in the offering. Stabilizing transactions consist of various bids for or purchases of common stock made by the underwriters in the open market prior to the completion of the offering.

The underwriters may also impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the representatives have repurchased shares sold by or for the account of such underwriter in stabilizing or short covering transactions.

Purchases to cover a short position and stabilizing transactions, as well as other purchases by the underwriters for their own account, may have the effect of preventing or retarding a decline in the market price of the company’s stock, and together with the imposition of the penalty bid, may stabilize, maintain or otherwise affect the market price of the common stock. As a result, the price of the common stock may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued at any time. These transactions may be effected on the New York Stock Exchange, in the over-the-counter market or otherwise.

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The underwriters do not expect sales to discretionary accounts to exceed five percent of the total number of shares offered.

We estimate that our share of the total expenses of the offering, excluding underwriting discounts and commissions, will be approximately $367,631. The Operating Company will pay all of the expenses incurred by us in connection with this offering.

NMFC and the Operating Company have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act of 1933.

The underwriters and their respective affiliates are full-service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. Certain of the underwriters and their respective affiliates may, from time to time, perform various financial advisory and investment banking services for the company, for which they will receive customary fees and expenses. In addition, an affiliate of Wells Fargo Securities, LLC is a lender under our Credit Facilities.

In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers and such investment and securities activities may involve securities and/or instruments of the issuer. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

The principal business address of Goldman, Sachs & Co. is 200 West Street, New York, New York 10282, the principal business address of Wells Fargo Securities, LLC is 375 Park Avenue, New York, New York 10152 and the principal business address of Morgan Stanley & Co. LLC is 1585 Broadway, New York, New York 10036.

Each of the underwriters may arrange to sell common shares offered hereby in certain jurisdictions outside the United States, either directly or through affiliates, where they are permitted to do so. In that regard, Wells Fargo Securities, LLC may arrange to sell shares in certain jurisdictions through an affiliate, Wells Fargo Securities International Limited, or WFSIL. WFSIL is a wholly-owned indirect subsidiary of Wells Fargo & Company and an affiliate of Wells Fargo Securities, LLC. WFSIL is a United Kingdom incorporated investment firm regulated by the Financial Services Authority. Wells Fargo Securities is the trade name for certain corporate and investment banking services of Wells Fargo & Company and its affiliates, including Wells Fargo Securities, LLC and WFSIL.

European Economic Area

Each underwriter has represented and agreed that, in relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a “Relevant Member State”), with effect from and including the date on which the Prospectus Directive is implemented in that Relevant Member State (the “Relevant Implementation Date”), it has not made and will not make an offer of shares to the public in that Relevant Member State prior to the publication of a prospectus in relation to the shares which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, with effect from and including the Relevant Implementation Date, make an offer of shares to the public in that Relevant Member State at any time:

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representatives nominated by NMFC for any such offer; or

provided that no such offer of shares shall require NMFC or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Directive.

For the purposes of this provision, the expression an “offer of shares to the public” in relation to any shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase or subscribe for the shares, as the same may be varied in that Relevant Member State by any measure implementing the Prospectus Directive in that Relevant Member State; “Prospectus Directive” means European Council Directive 2003/71/EC (and amendments thereto, including the 2010 PD Amending Directive) and includes any relevant implementing measure in the Relevant Member State; and “2010 PD Amending Directive” means Directive 2010/73/EU.

United Kingdom

Each underwriter has represented and agreed that:

(a) it has only communicated or caused to be communicated and will only communicate or cause to be communicated an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the FSMA) received by it in connection with the issue or sale of the shares in circumstances in which Section 21(1) of the FSMA would not, if the Issuer was not an authorized person, apply to the Issuer; and

(b) it has complied and will comply with all applicable provisions of the FSMA with respect to anything done by it in relation to the shares in, from or otherwise involving the United Kingdom.

Switzerland

This document does not constitute a prospectus within the meaning of Art. 652a of the Swiss Code of Obligations. The shares of common stock may not be sold directly or indirectly in or into Switzerland except in a manner which will not result in a public offering within the meaning of the Swiss Code of Obligations. Neither this document nor any other offering materials relating to the shares of common stock may be distributed, published or otherwise made available in Switzerland except in a manner which will not constitute a public offer of the shares of common stock in Switzerland.

Hong Kong

The shares may not be offered or sold by means of any document other than (i) in circumstances which do not constitute an offer to the public within the meaning of the Companies Ordinance (Cap.32, Laws of Hong Kong), or (ii) to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap.571, Laws of Hong Kong) and any rules made thereunder, or (iii) in other circumstances which do not result in the document being a “prospectus” within the meaning of the Companies Ordinance (Cap.32, Laws of Hong Kong), and no advertisement, invitation or document relating to the shares may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder.

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Singapore

This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares are subscribed or purchased under Section 275 by a relevant person which is: (a) a corporation (which is not an accredited investor) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or (b) a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary is an accredited investor, shares, debentures and units of shares and debentures of that corporation or the beneficiaries’ rights and interest in that trust shall not be transferable for 6 months after that corporation or that trust has acquired the shares under Section 275 except: (1) to an institutional investor under Section 274 of the SFA or to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA; (2) where no consideration is given for the transfer; or (3) by operation of law.

Japan

The securities have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (the Financial Instruments and Exchange Law) and each underwriter has agreed that it will not offer or sell any securities, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to a resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the Financial Instruments and Exchange Law and any other applicable laws, regulations and ministerial guidelines of Japan.

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LEGAL MATTERS

Certain legal matters in connection with the securities offered hereby will be passed upon for us by Sutherland Asbill & Brennan LLP, Washington, District of Columbia. Certain legal matters in connection with the securities offered hereby will be passed upon for the underwriters by Fried, Frank, Harris, Shriver & Jacobson LLP, New York, New York.

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

With respect to the unaudited interim financial information of New Mountain Finance Holdings, L.L.C. as of March 31, 2012 and for the periods ended March 31, 2012 and 2011, and of New Mountain Finance Corporation and New Mountain Finance AIV Holdings Corporation as of March 31, 2012 and for the three months then ended, which is included in this prospectus, Deloitte & Touche LLP, an independent registered public accounting firm, has applied limited procedures in accordance with the standards of the Public Company Accounting Oversight Board (United States) for a review of such information. However, as stated in their reports included in this prospectus, they did not audit and they do not express an opinion on that interim financial information. Accordingly, the degree of reliance on their reports on such information should be restricted in light of the limited nature of the review procedures applied. Deloitte & Touche LLP are not subject to the liability provisions of Section 11 of the Securities Act of 1933 for their reports on the unaudited interim financial information because those reports are not “reports” or a “part” of the Registration Statement prepared or certified by an accountant within the meaning of Sections 7 and 11 of the Act.

The financial statements of New Mountain Finance Holdings, L.L.C. as of December 31, 2011 and 2010 and for each of the three years ended December 31, 2011, and the financial statements of New Mountain Finance Corporation and New Mountain Finance AIV Holdings Corporation as of December 31, 2011 and for the period from May 19, 2011 (Commencement of Operations) to December 31, 2011, including the Senior Securities table included in the accompanying prospectus have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports appearing herein and elsewhere in the Registration Statement. Such financial statements and information included in the Senior Securities table as of December 31, 2011, 2010 and 2009 have been so included in reliance upon the reports of such firm, given their authority as experts in accounting and auditing.

The principal business address of Deloitte & Touche LLP is 2 World Financial Center, New York, New York 10281.

AVAILABLE INFORMATION

We have filed with the SEC a registration statement on Form N-2, together with all amendments and related exhibits, under the Securities Act, with respect to the shares of common stock offered by this prospectus supplement and the accompanying prospectus. The registration statement contains additional information about us and the shares of common stock being offered by this prospectus supplement and the accompanying prospectus.

We are required to file with or submit to the SEC annual, quarterly and current reports, proxy statements and other information meeting the informational requirements of the Exchange Act. You may inspect and copy these reports, proxy statements and other information, as well as the registration statement and related exhibits and schedules, at the Public Reference Room of the SEC at 100 F Street, N.E., Washington, District of Columbia 20549. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. The SEC maintains an internet site that contains reports, proxy and information statements and other information filed electronically by us with the SEC, which are available on the SEC’s website at http://www.sec.gov. Copies of these reports, proxy and information statements and other information may be

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obtained, after paying a duplicating fee, by electronic request at the following e-mail address: publicinfo@sec.gov, or by writing the SEC’s Public Reference Section, 100 F Street, N.E., Washington, District of Columbia 20549. This information will also be available free of charge by contacting us at 787 Seventh Avenue, 48th Floor, New York, New York 10019, by telephone at (212) 720-0300, or on our website at http://www.newmountainfinance.com. Information contained on our website or on the SEC’s web site about us is not incorporated into this prospectus supplement and the accompanying prospectus and you should not consider information contained on our website or on the SEC’s website to be part of this prospectus supplement and the accompanying prospectus.

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PROSPECTUS

New Mountain Finance Corporation

Common Stock

New Mountain Finance Corporation (“NMFC”) is a holding company with no direct operations of its own, and its only business and sole asset is its ownership of common membership units of New Mountain Finance Holdings, L.L.C. (the “Operating Company”). The Operating Company is an externally managed business development company managed by New Mountain Finance Advisers BDC, L.L.C. and is the operating company for NMFC’s business. NMFC and the Operating Company each have elected to be treated as a business development company under the Investment Company Act of 1940. The Operating Company’s investment objective is to generate current income and capital appreciation through the sourcing and origination of debt securities at all levels of the capital structure, including first and second lien debt, notes, bonds and mezzanine securities. NMFC owns approximately 34.6% of the common membership units of the Operating Company and New Mountain Finance AIV Holdings Corporation owns approximately 65.4% of the common membership units of the Operating Company.

NMFC may offer, from time to time, in one or more offerings, up to $150,000,000 of its common stock. The common stock may be offered at prices and on terms to be described in one or more supplements to this prospectus. In addition, this prospectus relates to 22,393,938 shares of NMFC’s common stock that may be sold by the selling stockholders identified under “Selling Stockholders”. Sales of NMFC’s common stock by the selling stockholders, which may occur at prices below the net asset value per share of NMFC’s common stock, may adversely affect the market price of NMFC’s common stock and may make it more difficult for NMFC to raise capital.

The offering price per share of NMFC’s common stock less any underwriting commissions or discounts will generally not be less than the net asset value per share of NMFC’s common stock at the time we make the offering. However, NMFC may issue shares of its common stock pursuant to this prospectus at a price per share that is less than its net asset value per share (i) with the prior approval of the majority of its common stockholders or (ii) under such other circumstances as the Securities and Exchange Commission may permit.

The selling stockholders identified under “Selling Stockholders” acquired their respective shares of NMFC’s common stock either through (i) the concurrent private placement to certain affiliates of NMFC in connection with NMFC’s initial public offering or (ii) the formation transactions completed immediately prior to NMFC’s initial public offering. Each offering by the selling stockholders of their shares of NMFC’s common stock through agents, underwriters or dealers will be accompanied by a prospectus supplement that will identify the selling stockholders that are participating in such offering. NMFC and the Operating Company will not receive any proceeds from the sale of shares of NMFC’s common stock by any of the selling stockholders.

NMFC’s common stock may be offered directly to one or more purchasers, or through agents designated from time to time by us, or to or through underwriters or dealers. The prospectus supplement relating to an offering will identify any agents or underwriters involved in the sale of NMFC’s common stock, and will disclose any applicable purchase price, fee, commission or discount arrangement between NMFC and its agents or underwriters or among NMFC’s underwriters or the basis upon which such amount may be calculated. See “Plan of Distribution”. NMFC may not sell any of its common stock through agents, underwriters or dealers without delivery of this prospectus and a prospectus supplement describing the method and terms of the offering of such common stock.

NMFC’s common stock is traded on the New York Stock Exchange under the symbol “NMFC”. On July 6, 2012, the last reported sales price on the New York Stock Exchange for NMFC’s common stock was $14.91 per share. Based on this last reported sales price of NMFC’s common stock, the aggregate market value of the shares of NMFC’s common stock held by the selling stockholders identified under “Selling Stockholders” is approximately $333.9 million.

An investment in NMFC’s common stock is very risky and highly speculative. Shares of closed-end investment companies, including business development companies, frequently trade at a discount to their net asset value. In addition, the companies in which NMFC invests, through the Operating Company, are subject to special risks. See “Risk Factors” beginning on page 19 to read about factors you should consider, including the risk of leverage, before investing in NMFC’s common stock.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

This prospectus may not be used to consummate sales of shares of common stock unless accompanied by a prospectus supplement.

Please read this prospectus and any accompanying prospectus supplements before investing and keep each for future reference. This prospectus and any accompanying prospectus supplements contain important information about NMFC and the Operating Company that a prospective investor ought to know before investing in NMFC’s common stock. NMFC and the Operating Company file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission (http://www.sec.gov), which is available free of charge by contacting NMFC by mail at 787 Seventh Avenue, 48th Floor, New York, New York 10019 or on our website at http://www.newmountainfinance.com.

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You should rely only on the information contained in this prospectus and any accompanying prospectus supplement. We have not authorized any dealer, salesman or other person to give any information or to make any representation other than those contained in this prospectus or any prospectus supplement to this prospectus. You must not rely upon any information or representation not contained in this prospectus or any such supplements as if we had authorized it. This prospectus and any such supplements do not constitute an offer to sell or a solicitation of any offer to buy any security other than the registered securities to which they relate, nor do they constitute an offer to sell or a solicitation of an offer to buy any securities in any jurisdiction to any person to whom it is unlawful to make such an offer or solicitation in such jurisdiction. The information contained in this prospectus and any such supplements is accurate as of the dates on their covers. Our business, financial condition, results of operations and prospects may have changed since then.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we have filed with the Securities and Exchange Commission (“SEC”), using the “shelf” registration process. Under the shelf registration process, which constitutes a delayed offering in reliance on Rule 415 under the Securities Act of 1933, as amended (the “Securities Act”), NMFC may offer, from time to time, in one or more offerings, up to $150,000,000 of its common stock on terms to be determined at the time of the offering. In addition, this prospectus relates to 22,393,938 shares of NMFC’s common stock that may be sold by the selling stockholders identified under “Selling Stockholders”. The shares may be offered at prices and on terms described in one or more supplements to this prospectus. This prospectus provides you with a general description of the offerings of shares that NMFC may conduct pursuant to this prospectus. Each time NMFC uses this prospectus to offer shares, we will provide a prospectus supplement that will contain specific information about the terms of that offering. A prospectus supplement may also add, update or change information contained in this prospectus.

Please carefully read this prospectus and any such supplements together with any exhibits and the additional information described under “Available Information” and in the “Summary” and “Risk Factors” sections before you make an investment decision.

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FEES AND EXPENSES

The following table is intended to assist you in understanding the costs and expenses that you will bear directly or indirectly. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus contains a reference to fees or expenses paid by “you”, “NMFC”, the “Operating Company”, or “us” or that “we”, “NMFC”, or the “Operating Company” will pay fees or expenses, stockholders will indirectly bear such fees or expenses through NMFC’s investment in the Operating Company.

Example

The following example, required by the SEC, demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in NMFC’s common stock. In calculating the following expense amounts, we have assumed that our borrowings and annual operating expenses would remain at the levels set forth in the table above. In the event that shares to which this prospectus relates are sold to or through underwriters, a corresponding prospectus supplement will restate this example to reflect the applicable sales load and offering expenses.

The example and the expenses in the tables above should not be considered a representation of future expenses, and actual expenses may be greater or less than those shown.

While the example assumes, as required by the applicable rules of the SEC, a 5.0% annual return, our performance will vary and may result in a return greater or less than 5.0%. The incentive fee under the Investment Management Agreement, which, assuming a 5.0% annual return, would either not be payable or would have an insignificant impact on the expense amounts shown above, is not included in the above example. The above illustration assumes that we will not realize any capital gains (computed net of all realized capital losses and unrealized capital depreciation) in any of the indicated time periods. If we achieve sufficient returns on our investments, including through the realization of capital gains, to trigger an incentive fee of a material amount, our expenses and returns to our investors would be higher. For example, if we assumed that we received our 5.0% annual return completely in the form of net realized capital gains on our investments, computed net of all cumulative unrealized depreciation on our investments, the projected dollar amount of total cumulative expenses set forth in the above illustration would be as follows:

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The example assumes no sales load. In addition, while the examples assume reinvestment of all distributions at net asset value, participants in NMFC’s dividend reinvestment plan will receive a number of shares of NMFC’s common stock determined by dividing the total dollar amount of the distribution payable to a participant by the market price per share of NMFC’s common stock at the close of trading on the dividend payment date. The market price per share of NMFC’s common stock may be at, above or below net asset value. See “Dividend Reinvestment Plan” for additional information regarding the dividend reinvestment plan.

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SELECTED FINANCIAL AND OTHER DATA

The selected financial data should be read in conjunction with the respective financial statements and related combined notes thereto and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included in this prospectus. Financial information for the years ended December 31, 2011, December 31, 2010, December 31, 2009 and for the period October 29, 2008 (commencement of operations) to December 31, 2008 has been derived from our financial statements that were audited by Deloitte & Touche, LLP, an independent registered public accounting firm. The financial information at and for the three months ended March 31, 2012 was derived from our unaudited financial statements and related notes. In the opinion of management, all adjustments, consisting solely of normal recurring accruals, considered necessary for the fair presentation of financial statements for the interim periods, have been included. Our results for the interim period may not be indicative of our results for the full year. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Senior Securities” below for more information.

(in thousands except shares and per share data)

N/A—Fund was not unitized as of December 31, 2010, December 31, 2009 and December 31, 2008.

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NM—Total return from commencement of operations through December 31, 2008 was deemed not meaningful due to the scaling of operations during this short time period.

(in thousands except shares and per share data)

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SELECTED QUARTERLY FINANCIAL DATA

The following table sets forth certain quarterly financial data for the quarter ended March 31, 2012 and for each of the quarters for the fiscal years ended December 31, 2011, December 31, 2010 and December 31, 2009 of the Operating Company and for the quarter ended March 31, 2012 and for each of the quarters from May 19, 2011 (commencement of operations) through December 31, 2011 of NMFC. This data is derived from our unaudited financial statements. Results for any quarter are not necessarily indicative of results for the full year or for any future quarter.

The below selected quarterly financial data is for the Operating Company.

(in thousands except for per unit data)