Professional services firm Aon has announced it will acquire middle-market insurer USI from its private equity owners for $17 billion to become one of the US’s leading players in the sector.

The deal, one of the largest insurance buyouts in recent years, continues a pattern of consolidation in the market as companies work to bolster their market presence.

USI is currently the tenth largest insurance broker in the country, bringing in around $3 billion in annual revenue and employing over 10,500 people. Aon said that its proprietary USI ONE analytics and planning platform is highly complementary with its existing strategy and technology engine.

The acquisition marks its second multi-billion-dollar middle-market deal this decade, following its $13 billion purchase of property and casualty broker NFP in 2024.

Greg Case, president and chief executive of Aon, said: “Combining with USI will establish the premier US middle-market platform, deepen our context advantage and position Aon to accelerate organic growth.

“Building on the success of our acquisition of NFP, USI will substantially enhance our middle-market footprint and expand access for our firm in the [excess and surplus] segment to deliver content, capabilities and expertise to a broader client base, while enabling client leaders to expand relationships and win new business.”

The US middle-market insurance segment is worth more than $40 billion and accounts for over a third of commercial property and casualty premiums in the country.

Aon’s shares fell six per cent in early trading after the news on Monday and are down nearly four per cent since the start of the year.

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