UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of report (Date of earliest event reported) February 27, 2018

Marsh & McLennan Companies, Inc.

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code (212) 345-5000

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

☐  Emerging growth company

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

On February 27, 2018, Marsh & McLennan Companies, Inc. (the “Company”) entered into an Underwriting Agreement (attached hereto as Exhibit 1.1 and incorporated herein by reference) with Citigroup Global Markets Inc. and Goldman Sachs & Co. LLC, as representatives of the several underwriters named therein (the “Underwriters”), pursuant to which the Underwriters agreed to purchase from the Company $600,000,000 aggregate principal amount of its 4.200% senior notes due 2048 (the “Notes”).

The Notes were offered and sold pursuant to the Company’s effective shelf registration statement (the “Registration Statement”) on Form S-3 (Registration No. 333-206217) under the Securities Act of 1933, as amended, filed with the Securities and Exchange Commission on August 7, 2015, and a prospectus supplement dated February 27, 2018.

The Notes were issued on March 1, 2017 pursuant to the Indenture dated July 15, 2011, by and between the Company and The Bank of New York Mellon, as trustee (the “Trustee”), filed as Exhibit 4.1 to the Company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2011, as supplemented by an Tenth Supplemental Indenture by and between the Company and the Trustee (attached hereto as Exhibit 4.1 and incorporated herein by reference). The form of the Notes is attached hereto as Exhibit 4.2 and is incorporated herein by reference.

On February 27, 2018, the Company issued a press release announcing the pricing of the Notes. A copy of the press release is attached hereto as Exhibit 99.1.

A copy of the opinion of Davis Polk & Wardwell LLP, counsel to the Company, relating to the legality of the Notes is filed as Exhibit 5.1 hereto.

(d) Exhibits

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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