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Marsh McLennan is a professional services firm that helps businesses buy insurance, manage risk, and get consulting advice.
Marsh McLennan is the world's biggest insurance broker. Most people never deal with it directly, but it sits quietly in the middle of the global economy, helping companies of every size buy the insurance they need and figure out how much risk they can stomach.
The firm runs four main businesses. Marsh, the biggest, is the insurance broker: it shops the market on behalf of corporate clients and places their coverage with insurers, earning commissions and fees for the matchmaking. Guy Carpenter does the same job for reinsurance — insurance for insurance companies — while Oliver Wyman provides management consulting, and Mercer advises companies on employee benefits, pensions, and investments. The client pays for expertise and access, and sticks around because switching brokers mid-policy is a hassle and the advice is genuinely hard to replicate at scale. What makes the business tick is that it doesn't take on much insurance risk itself. It gets paid mostly in fees and commissions for arranging coverage, so it makes money whether or not a client ever files a claim. That steady, fee-based model throws off reliable cash, which the company returns to shareholders through dividends and buybacks and uses to buy smaller rivals — it has done dozens of these deals over the decades, including its 2019 purchase of Jardine Lloyd Thompson for about $5.6 billion. The whole thing traces back to 1871, when a young Chicago insurance clerk named Henry Marsh started his own agency, and it grew into a giant through relentless acquisitions.
The obvious vulnerability is that it lives on insurance prices: when premiums are rising, commissions swell, and when the market softens, growth slows. Rivals like Aon and Arthur J. Gallagher fight for the same corporate clients, and technology is slowly letting companies compare and buy coverage more cheaply. Still, scale matters enormously in this game — the biggest broker gets the best access to insurers and the deepest data on what coverage should cost — and Marsh McLennan has been near the top of that pile for a very long time.
Saved answer · last researched 15 Nov 2026