Insurance Brokerage Mega-Deals: Gallagher, Aon, Marsh, and Brown & Brown

Introduction

Since late 2023 the insurance brokerage industry has lived through the most concentrated run of mega-deals in its history. Five transactions worth over $61 billion have transformed the competitive landscape: Aon-USI ($17 billion, pending), Gallagher-AssuredPartners ($13.5 billion), Aon-NFP ($13 billion), Brown & Brown-Accession ($9.8 billion), and Marsh McLennan-McGriff ($7.75 billion). Unlike bank M&A, which is driven by regulatory capital and deposit franchise economics, insurance brokerage consolidation is driven by the EBITDA multiple arbitrage between small agencies (4-5x) and institutional platforms (14-17x), PE portfolio exit timing, and the structural advantages of scale in a fragmented industry. For FIG bankers, these transactions represent some of the largest advisory mandates in the FIG deal flow universe.

Aon-USI ($17 billion, announced August 31, 2026, closing targeted for the fourth quarter of 2026) is the largest insurance brokerage acquisition on record, setting aside the abandoned Aon-Willis merger. Aon agreed to buy USI, the tenth-largest US broker with about $3 billion in annual revenue and more than 10,500 employees, from KKR and its co-investors in an all-cash deal funded with new debt. Aon's announcement prices it at about 14.5x trailing adjusted EBITDA including roughly $395 million of run-rate synergies. USI is Aon's second middle-market platform after NFP, the clearest case yet of a strategic broker buying scale that private equity built.

Gallagher-AssuredPartners ($13.5 billion, announced December 2024, closed August 2025) was the largest insurance brokerage acquisition ever completed when it closed. Arthur J. Gallagher acquired AssuredPartners, a PE-backed platform (GTCR and Apax Partners) with $2.9 billion in trailing revenue, approximately 10,900 employees, and over 400 offices across the US, UK, and Ireland. The valuation of 14.3x pro forma EBITDAC (net 11.3x after a $1 billion deferred tax asset) reflected AssuredPartners' position as a fully scaled platform that had already completed over 500 tuck-in acquisitions.

EBITDAC

EBITDAC (Earnings Before Interest, Taxes, Depreciation, Amortization, and Change in Contingent Consideration) is the primary profitability metric for insurance brokerages. It adjusts standard EBITDA for changes in the fair value of contingent consideration (earn-outs) from prior acquisitions, which are a recurring feature of roll-up platforms that acquire dozens to hundreds of agencies annually, and it is the denominator in brokerage valuation multiples (EV/EBITDAC). For large public brokers like Gallagher, Aon, and Marsh, EBITDAC margins typically range from 30-35%, reflecting the capital-light, fee-based business model where the primary cost is compensation for producers (brokers who originate and manage client relationships).

Aon-NFP ($13 billion, announced December 2023, closed April 2024) was the first mega-deal to close and the catalyst for the wave. Aon acquired NFP Corp, a middle-market property and casualty, benefits, wealth management, and retirement advisory platform with over 7,700 employees. The consideration comprised approximately $7 billion in cash and assumed liabilities plus $6 billion in equity (19 million Aon shares). NFP completed 27 middle-market acquisitions in 2024 alone.

Brown & Brown-Accession ($9.8 billion, announced June 2025, closed August 2025) added the Accession Risk Management Group (parent of Risk Strategies and One80 Intermediaries) to Brown & Brown's franchise. The combined entity incorporates over 5,000 insurance professionals and $1.7 billion in pro forma 2024 adjusted revenue. Risk Strategies joins Brown & Brown's retail segment, while One80 Intermediaries joins a newly created specialty distribution segment, reflecting the strategic importance of wholesale and MGA channels.

Marsh McLennan-McGriff ($7.75 billion, all cash, announced September 2024, closed November 2024) added McGriff Insurance Services (an affiliate of TIH) with $1.3 billion in trailing twelve-month revenue and approximately 3,500 employees. McGriff enhances Marsh's commercial property and casualty, employee benefits, management liability, and personal lines capabilities.

Three forces converged to produce this unprecedented concentration of mega-deals.

PE portfolio exits reached critical mass. AssuredPartners, the largest of these targets to have closed, was a franchise GTCR and Apax Partners had spent over a decade building through 500+ acquisitions. The platform had reached a scale where further tuck-in acquisitions generated diminishing marginal returns relative to the platform's size, and the PE sponsors needed liquidity. Gallagher was the natural strategic exit partner. GTCR realized 3x+ returns from its 2019 recapitalization. Similar dynamics applied to the other targets: NFP was backed by Madison Dearborn Partners, Risk Strategies had PE backing, and USI has been backed by KKR since 2017. KKR's release on the USI sale cites a 3.4x return on the balance sheet capital it invested over the life of the holding. The 2024-2026 window offered favorable conditions (strong insurance market, low credit losses, willing strategic buyers) for PE exits at premium multiples.

Market share pressure from PE-backed consolidators. The rise of PE-backed platforms like Hub International ($29 billion valuation), Acrisure ($32 billion), and Alliant (about $5.8 billion of 2025 revenue) had eroded the public brokers' competitive position. Private capital-backed buyers made 75.1% of announced US brokerage acquisitions through August 2026, and the ten most active buyers 52.2%, according to MarshBerry's August 2026 deal review. The mega-deals were a strategic response: reclaim market share through transformational acquisitions rather than competing agency-by-agency against PE platforms with higher leverage tolerance and faster decision-making.

Scale advantages in compliance and technology. State-by-state licensing, surplus lines tax filings, fiduciary mandates, and cybersecurity requirements create disproportionate compliance costs for mid-market firms. Larger platforms automate these workflows across thousands of accounts, achieving structural cost advantages. Data analytics, AI-driven placement optimization, and digital client portals similarly benefit from scale, as the fixed investment is spread across a larger revenue base. Technology also cuts the other way: in the February 9, 2026 sell-off after an AI insurance-comparison app launched inside ChatGPT, WTW fell 12%, Gallagher 9.9% and Aon 9.3% in a day, showing how AI disintermediation fears can compress the public broker multiples that anchor deal pricing (see how AI is reshaping financial services).

The mega-deals have significantly consolidated the top of the market. Marsh McLennan led AM Best's global broker ranking for the 16th consecutive year with $27.0 billion of 2025 revenue, followed by Aon at $17.2 billion and Gallagher at $13.9 billion, with only four and a half months of AssuredPartners included. On US-sourced revenue, Business Insurance's 2026 ranking shows Gallagher passing Aon for second place ($8.8 billion versus $8.2 billion); adding USI's $2.9 billion would put Aon back in front.

The competitive implications extend beyond the mega-deal participants. Mid-market brokers (those with $50 million to $500 million in revenue) face a strategic decision: grow aggressively through PE-backed acquisition to reach defensible scale, or sell to a larger platform while valuations remain elevated. Below them, the tuck-in market is thinning: OPTIS Partners counted 292 agency deals in the first half of 2026, the slowest start to a year since 2016, even as Aon-USI set a price record. The result is a bifurcated market, with record platform trades at the top, fewer and more selective agency acquisitions below, and the independent middle tier absorbed in both directions.

Each mega-deal presents distinct integration challenges. Gallagher estimated $500 million in integration costs over three years (including $200 million in non-cash retention awards) and plans to increase its acquisition pace to 100+ deals per year post-close, nearly double its prior 50-60 annual pace. Aon's NFP integration deliberately preserved NFP's operational independence (the "independent and connected" model) to avoid disrupting the middle-market culture that drives organic growth and producer retention. USI raises the stakes: Aon plans to run both platforms as one middle-market business under USI chief executive Mike Sicard.

The talent retention challenge is significant. Insurance brokerage is a relationship business where top producers generate disproportionate revenue. Large-scale acquisitions risk prompting departures to independent firms or competitors, particularly if producers perceive reduced autonomy or unfavorable compensation changes. Gallagher's retention awards reflect the recognition that human capital, not physical infrastructure, is the primary asset being acquired.

The insurance brokerage mega-deal wave is the most visible example of a broader pattern in FIG M&A: capital-light, fee-based financial services businesses attracting transformational deal activity driven by scale economics, PE exit dynamics, and the structural attractiveness of recurring revenue streams. The advisory mandates generated by these transactions (sell-side for PE sponsors, buy-side for strategic acquirers, fairness opinions, antitrust advisory) are among the most lucrative in the FIG banker's toolkit.