The Fairfax business prevails in an auction run by Willis.
The Pioneer deal marks K2's first international acquisition.
The deal struck last July included two performance-linked payments.
The acquisition will help scale its platform, modernise its products and explore acquisition opportunities.
The Digital Partners CEO says funding struggles among small InsurTechs present acquisition opportunities for the carrier’s larger partners.
The first signs are also emerging of distressed acquisition opportunities, the executive said.
The deal was awaiting regulatory approval from the CDI after the deal was agreed in August.
Members will work with the existing integration leadership team.
Capital Returns' Ron Bobman said the firm had "a complete absence of competitive advantages”.
At least one other PE house is understood to remain in the process.
The purchase expands the broker’s offering in the American professional sports space.
The action follows similar moves by AM Best and Fitch after a proposed $9bn sale was dropped.