Cover and table of contents

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

(Mark One)

For the fiscal year ended December 31, 2020

OR

Commission File No. 1-5998

Marsh & McLennan Companies, Inc.

(Exact name of registrant as specified in its charter)

1166 Avenue of the Americas

New York, New York 10036-2774

(Address of principal executive offices; Zip Code)

(212) 345-5000

Registrant’s telephone number, including area code

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

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ý No ¨

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ¨ No ý

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý No ¨

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ý No ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting Company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting Company" in Rule 12b-2 of the Exchange Act. (Check one):

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. ☐

Indicate by check mark whether the registrant is a shell Company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ý

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. Yes ☒ No ¨

As of June 30, 2020, the aggregate market value of the registrant's common stock held by non-affiliates of the registrant was approximately 53,818,358,381 computed by reference to the closing price of such stock as reported on the New York Stock Exchange on June 30, 2020.

As of February 12, 2021, there were outstanding 508,186,561 shares of common stock, par value $1.00 per share, of the registrant.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of Marsh & McLennan Companies, Inc.’s Notice of Annual Meeting and Proxy Statement for the 2021 Annual Meeting of Stockholders (the "2021 Proxy Statement") are incorporated by reference in Part III of this Form 10-K.

INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K contains "forward-looking statements," as defined in the Private Securities Litigation Reform Act of 1995. These statements, which express management's current views concerning future events or results, use words like "anticipate," "assume," "believe," "continue," "estimate," "expect," "intend," "plan," "project" and similar terms, and future or conditional tense verbs like "could," "may," "might," "should," "will" and "would."

Forward-looking statements are subject to inherent risks and uncertainties that could cause actual results to differ materially from those expressed or implied in our forward-looking statements. Factors that could materially affect our future results include, among other things:

• the financial and operational impact of COVID-19 on our revenue and ability to generate new business, our overall level of profitability and cash flow, and our liquidity, including the timeliness and collectability of our receivables;

• the impact from lawsuits, other contingent liabilities and loss contingencies arising from errors and omissions, breach of fiduciary duty or other claims against us, including claims related to pandemic coverage;

• the impact of investigations, reviews, or other activity by regulatory or law enforcement authorities, including the ongoing U.K. FCA review of legacy JLT enhanced transfer value advice;

• the financial and operational impact of complying with laws and regulations where we operate and the risks of noncompliance with such laws, including anti-corruption laws such as the U.S. Foreign Corrupt Practices Act, U.K. Anti-Bribery Act, trade sanctions regimes and cybersecurity and data privacy regulations such as the E.U.’s General Data Protection Regulation;

• our ability to maintain adequate safeguards to protect the security of our information systems and confidential, personal or proprietary information, particularly given the increased risk of supply chain attacks and other cybersecurity attacks or unauthorized dissemination of information caused by remote work arrangements;

• our ability to compete effectively and adapt to changes in the competitive environment, including to respond to technological change, disintermediation, digital disruption and other types of innovation;

• our ability to manage risks associated with our investment management and related services business, particularly in the context of uncertain equity markets, including our ability to execute timely trades in light of increased trading volume and to manage potential conflicts of interest between investment consulting and fiduciary management services;

• our ability to attract and retain industry leading talent;

• our ability to successfully recover if we experience a business continuity problem due to cyberattack, natural disaster, government unrest or otherwise;

• the regulatory, contractual and reputational risks that arise based on insurance placement activities and various insurer revenue streams; and

• the impact of changes in tax laws, guidance and interpretations, or disagreements with tax authorities, particularly due to the change in U.S. presidential administration.

The factors identified above are not exhaustive. Further information concerning Marsh & McLennan Companies and its businesses, including information about factors that could materially affect our results of operations and financial condition, is contained in the Company's filings with the Securities and Exchange Commission, including the "Risk Factors" section in Part I, Item 1A of this report and the "Management’s Discussion and Analysis of Financial Condition and Results of Operations" section in Part II, Item 7 of this report. We caution readers not to place undue reliance on any forward-looking statements, which are based only on information currently available to us and speak only as of the dates on which they are made. We undertake no obligation to update or revise any forward-looking statement to reflect events or circumstances arising after the date on which it is made.

i

TABLE OF CONTENTS

ii

PART I