Liberty Mutual Insurance Group has acquired Hughes Insurance, which employs 300 people across Northern Ireland.
Liberty said it expected the deal to be completed at the beginning of July 2015, with its Irish subsidiary becoming the lead underwriter of Hughes from next month.
Gareth Brady will continue as chief executive of Hughes Insurance, according to a statement, with the rest of the company's management team also remaining in their positions.
Hughes provides one in every five motor insurance policies sold in Northern Ireland, according to Liberty, and has £60m in gross written premium across a number of insurance categories for the year to the end of March.
The acquisition brings to 1,800 the number of people employed by Liberty Insurance across the island of Ireland.