Abbey Insurance has bought rival firm Open and Direct.
It nearly doubles the size of the Carrickfergus-based broker from more than 220 staff to more than 400.
Open and Direct operates 13 branches and Abbey 15.
Since 2009 Open and Direct had been owned by the UK-based Swinton Insurance Group. All Open and Direct staff have transferred across to Abbey.
Trevor Shaw, chief executive of Abbey, said: “We are very pleased that through this acquisition, we have almost doubled the size of the Abbey Insurance Brokers business and extended our branch network right across Northern Ireland.
“Over 40-plus years in the local market, Abbey Insurance has built a very strong business, focused on customer service excellence, which is demonstrated in the fact that almost 90% of our customers return to us year after year.
“In order to secure significant further growth, we recognised the need to acquire another business. We looked carefully at Open and Direct and considered it to be a good fit with Abbey, in terms of its professional local staff, the strength of its operation and its geographical footprint.
“Through this newly increased scale and the associated buying power, Abbey Insurance will continue to search for the very best insurance deals for all of our customers, now with an even broader range of insurance providers.”
The deal was financed by Ulster Bank.
Kenton Hilman, head of corporate and property banking at Ulster Bank, said: “We are delighted to support Abbey Insurance in their plans for sustainable growth.
“This acquisition is an important step in that strategy, and we are happy to be working closely with them to assist a growing local business in further developing its presence.”