Aviva Ireland said it has completed the deal to buy life insurer Friends First after the Central Bank gave its approval last week.
The transaction had already received approval from the Competition and Consumer Protection Commission (CCPC) in February.
The completion of the deal will see Aviva become one of the largest composite insurers in Ireland.
It market share in life insurance will increase to 15%, alongside its existing 15% market share in general insurance.
Aviva first announced its intention to acquire Friends First Life Assurance Company from Dutch insurer Achmea last November.
The company said that work on the integration of the two businesses is underway and the process is expected to be completed by mid 2020.
It will trade under the Aviva brand from January 2019.
Over the coming weeks, Aviva said it will write to over 250,000 customers joining from Friends First to welcome them and to tell them they do not need to take any action as a result of the change in ownership.