How a Chicago Fire survivor became the world's largest insurance brokerage powerhouse
Marsh McLennan began in the ashes of the Great Chicago Fire of 1871. Today, it stands as a global behemoth, dominating insurance brokerage and consulting. From surviving the 9/11 tragedy to navigating massive bid-rigging scandals, the firm’s evolution reveals how professional services giants scale through relentless acquisition and strategic pivots.
The firm traces its roots to 1905, when Henry W. Marsh and Donald R. McLennan merged their Chicago-based operations. Marsh had established his business in 1871, a period marked by the collapse of numerous insurers following the Great Chicago Fire. By 1962, the company had gone public, and by 1969, it adopted a holding company structure to manage its diverse service offerings under distinct banners.
Growth has been driven by aggressive expansion. In 1997, the company acquired Johnson & Higgins for $1.8 billion, a move that reclaimed its position as the world's largest insurance broker. More recently, the firm has continued its consolidation strategy, acquiring Jardine Lloyd Thompson in 2019 for £4.3 billion and McGriff Insurance Services in 2024 for $7.75 billion. These moves reflect a long-standing focus on risk management and human capital, often shedding non-core assets like Putnam Investments, which was sold for $3.9 billion in 2007.
The firm’s history is also defined by profound challenges. On September 11, 2001, the company suffered a devastating loss when its offices in the North Tower of the World Trade Center were destroyed, resulting in the deaths of 295 employees and 63 contractors. Later, in 2004, the firm faced a major bid-rigging scandal involving New York Attorney General Eliot Spitzer. The company settled for $850 million in 2005, subsequently reorganizing its operations to emphasize transparency and core consulting services.
Today, Marsh McLennan operates through four primary units: Marsh, Marsh Re, Mercer, and Oliver Wyman. As of 2025, risk and insurance services remain the company's financial engine, accounting for 63% of total revenue and 71% of operating profit. Now ranked 175th on the Fortune 500, the firm continues to refine its identity, rebranding its subsidiaries as Marsh in 2025 to streamline its global market presence.
Source: Marsh McLennan
