The deal, whose financial terms were not revealed, was first announced by the bank in March this year.
Capstone specialises in mergers and acquisitions, capital advisory, financial advisory and special situations and restructuring.
The acquisition is expected to expand Huntington’s regional banking foundation with the addition of two main offices in Boston and Denver and additional offices in 12 US cities including Chicago, Dallas, Detroit, Los Angeles, New York and Philadelphia.
Capstone is also expected to bolster Huntington’s capabilities to cater to middle market business owners throughout the corporate lifecycle.
Following the transaction, the two companies will offer a unified set of banking solutions across traditional commercial banking, investment banking and capital markets, specifically tailored for private business owners.
Huntington Commercial Banking senior executive vice president and co-president Scott Kleinman said: “The combined industry expertise of Huntington and Capstone, along with our ability to serve our growing core middle market client base across the United States, enables us to expand our role as a trusted advisor to a wide variety of businesses.
“Our industry insights and full range of capabilities position us to provide a consistent, differentiated experience for our Internal Use clients, who will benefit from an aligned culture that puts customers and communities at the centre of everything we do.”
Capstone Partners founder and president John Ferrara added: “Our combination will accelerate Capstone’s plans for continued growth while also bolstering Huntington’s banking verticals, especially in sponsor finance, healthcare, technology and telecom, and industrials.”