Free Writing Prospectus (Form FWP)

Final Term Sheet Filed Pursuant to Rule 433 Supplementing the Preliminary Prospectus

Supplement, dated October 19, 2026

Registration Statement No. 333-280979

October 20, 2026

Marsh & McLennan Companies, Inc.

€600,000,000 aggregate principal amount of 4.250% Senior Notes due 2032 (the "2032 Notes")

€600,000,000 aggregate principal amount of 4.625% Senior Notes due 2036 (the "2036 Notes" and, together with the 2032 Notes, the "Notes")

Terms Applicable to the Notes

Terms Applicable to the 2032 Notes

Terms Applicable to the 2036 Notes

Neither of Moody's Investors Service, Inc. ("Moody's") or S&P Global Ratings, acting through Standard & Poor's Financial Services LLC ("S&P"), is established in the European Union nor registered in accordance with Regulation (EC) No. 1060/2009 on credit rating agencies, as amended (the "CRA Regulation"), and therefore is not included in the list of credit rating agencies published by the European Securities and Markets Authority ("ESMA") on its website in accordance with the CRA Regulation; however, the ratings assigned by each of Moody's and S&P are endorsed in the European Union by Moody's Investors Service Ltd. and S&P Global Ratings Europe Limited, respectively.

The Issuer has filed a registration statement, including a prospectus and a related preliminary prospectus supplement, with the SEC for the offering to which this communication relates. Before you invest, you should read the preliminary prospectus supplement, the prospectus in the registration statement and other documents the issuer has filed with the SEC for more complete information about the issuer and this offering. You may get these documents for free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, the Joint Book-Running Managers will arrange to send you the prospectus and prospectus supplement if you request it by contacting: (i) Merrill Lynch International at 1-800-294-1322, (ii) Deutsche Bank AG, London Branch toll-free at 1-800-503-4611, (iii) Barclays Bank PLC toll-free at 1-888-603-5847 and (iv) HSBC Bank plc toll-free at 1-866-811-8049.

This communication should be read in conjunction with the preliminary prospectus supplement and the accompanying prospectus. The information in this communication supersedes the information in the preliminary prospectus supplement and the accompanying prospectus to the extent it is inconsistent with the information in such preliminary prospectus supplement or the accompanying prospectus. Terms used but not defined herein have the meanings given in the preliminary prospectus supplement.

Prohibition of Sales to EEA Retail Investors: The Notes are not intended to be offered, sold or otherwise made available to any retail investor in the European Economic Area, and no key information document required by Regulation (EU) No. 1286/2014 has been or will be prepared for offering or sale to retail investors in the European Economic Area.

Prohibition of Sales to UK Retail Investors: The Notes are not intended to be offered, sold, distributed or otherwise made available to any retail investor in the United Kingdom, and no disclosure document required by the FCA Product Disclosure Sourcebook has been or will be prepared for offering, selling or distribution to retail investors in the United Kingdom.

This document is only for distribution to and directed at: (i) in the UK, persons having professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (as amended) (the "Order") and high net worth entities falling within Article 49(2)(a) to (d) of the Order; (ii) persons who are outside the UK; and (iii) any other person to whom it can otherwise be lawfully distributed (all such persons together being referred to as "Relevant Persons"). Any investment or investment activity to which this document relates is available only to and will be engaged in only with Relevant Persons, and any person who is not a Relevant Person should not rely on it.

Target market assessment under MiFID II and the UK MiFIR: eligible counterparties and professional clients only; no retail distribution.

Any disclaimers or other notices that may appear below are not applicable to this communication and should be disregarded. Such disclaimers or other notices were automatically generated as a result of this communication being sent via Bloomberg or another email system.