South Wales brokers, Carlyle Insurance Brokers and the Johns' Bowen Partnership are merging.
The move is intended to expand the new firm's commercial general insurance which currently provides 75% of turnover. The remaining quarter focuses on independent financial advice.
Carlyle is the insurance broking subsidiary of Julian Hodge Bank. It is hoped that the bank's corporate customer base will provide the merger with an increased workload.
Supplementing each other's specialist areas should also develop business for the new group.
Director of Carlyle, George Wigley, said: "This new development reinforces Carlyle Insurance Brokers' position as a major subsidiary within the Julian Hodge Bank Group and its status as one of the UK's leading insurance brokers.
"Our customers will benefit from the pooling of specialist insurance advisers who are able to cater for the needs of all our existing and new insurance clients."
Carlyle has traditionally had commercial clients across Britain - it is especially strong in the South East - providing policies covering property development and landlord cover.
Johns' Bowen brings new business to the merger, providing television, film and broadcasting insurance.
Overall, Carlyle places commercial insurance risks for all sizes of businesses, covering manufacturing, services and retail sectors.
Following the amalgamation both companies have moved to Johns' Bowens' old Cardiff headquarters. The merger has not resulted in any redundancies.
Carlyle was established in 1975 but only saw expansion last year, on acquiring Churchgate Insurance.
Johns' Bowen was founded by the late Roger Johns in 1977. It developed its business throughout South Wales, offering a wide range of insurance broking services, eventually expanding its life, pensions and investment services during the late 1980s.