QuickLinks -- Click here to rapidly navigate through this document


EXHIBIT 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER
PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 (18 U.S.C. 1350)

        In connection with the Annual Report on Form 10-K for the period ended December 31, 2014 (the "Report") of New Mountain Finance Corporation (the "Registrant"), as filed with the United States Securities and Exchange Commission on the date hereof, I, Robert A. Hamwee, the Chief Executive Officer of the Registrant, hereby certify, to the best of my knowledge, that:

/s/ ROBERT A. HAMWEE

   
Name:   Robert A. Hamwee    
Date:   March 2, 2015    



QuickLinks

CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 (18 U.S.C. 1350)