Aon has confirmed a definitive agreement to acquire USI Insurance Services from private equity firm KKR for $17bn.

Aon said the deal bolsters its goal of targeting the US middle-market segment, building on its 2024 acquisition of NFP for $13bn. The acquisition also gives Aon expanded direct access to the excess and surplus (E&S) market through MGAs and MGUs, drawing on USI’s wholesale capabilities.

Greg Case, president and chief executive officer of Aon, said the combination would create a market-leading platform.

“Combining with USI will establish the premier U.S. middle-market platform, deepen our context advantage and position Aon to accelerate organic growth,” said Case. “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 E&S segment to deliver content, capabilities and expertise to a broader client base, while enabling client leaders to expand relationships and win new business.”

Under the agreement, USI chairman and chief executive officer Mike Sicard will serve as president of Aon and global chief executive officer of Middle Market once the deal closes, which is expected during the fourth quarter of 2026. The boards of both companies have approved the deal, and the brokers will continue to operate separately until the closing date. Aon said it will fund the transaction and related expenses with new debt.

Valhalla, New York-based USI is the tenth-largest US insurance broker, with about $3bn in annual revenue. The brokerage has around 200 offices across the US and a combined 10,500 employees. Its USI One analytics platform was a clear draw for Aon.

“[The combined Aon and USI platforms will] generate richer insight, advance the development of innovative, AI-driven solutions and expand the universe of insurable risk, while further reinforcing the context advantage that differentiates Aon,” Case added.

The deal marks the latest chapter in USI’s ownership history. KKR and Canadian pension fund Caisse de dépôt et placement du Québec agreed to buy the brokerage from Onex in 2017 in a $4.3bn deal. In 2023, KKR invested an additional $1bn in USI to become its largest shareholder.

Aon said it expects to deliver about $395m in annual run-rate net adjusted EBITDA from revenue and cost synergies. Aon is the third-largest broker in the US, behind Marsh and Arthur J. Gallagher, with about $8.15bn in revenue.