UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-A

FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES

PURSUANT TO SECTION 12(b) OR (g) OF

THE SECURITIES EXCHANGE ACT OF 1934

Affiliated Managers Group, Inc.

(Exact name of registrant as specified in its charter)

Securities to be registered pursuant to Section 12(b) of the Act:

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c) or (e), check the following box.  ☒

If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d) or (e), check the following box.  ☐

If this form relates to the registration of a class of securities concurrently with a Regulation A offering, check the following box.  ☐

Securities Act registration statement or Regulation A offering statement file number to which this form relates: 333-230423

Securities to be registered pursuant to Section 12(g) of the Act: None

INFORMATION REQUIRED IN REGISTRATION STATEMENT

This Registration Statement on Form 8-A relates to the 4.200% Junior Subordinated Notes due 2061 (the “Notes”) of Affiliated Managers Group, Inc. (the “Registrant”) and hereby incorporates by reference the description of the Notes set forth in (i) the section captioned “Description of the Debt Securities” in the Prospectus included in the Registrant’s Registration Statement on Form S-3 (File No. 333-230423), dated March 21, 2019 (the “Prospectus”), and (ii) the section captioned “Description of Notes” in the Prospectus Supplement, dated July 8, 2021 to the Prospectus.

2

SIGNATURE

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereto duly authorized.

3