Bristol & West is to sell its branch network to Britannia Building Society for about 150m.
The sale is expected to take a few months to complete and is subject to approval by the UK courts and FSA.
The Bristol & West brand and all other parts of the Bristol & West business will be retained by Bank of Ireland. There will be no compulsory redundancies as a result of the sale.
Bank of Ireland group chief executive Brian Goggin made it clear the branch network was to be disposed of last November.
The focus now for the group will be on growing the mortgage business, the banking operation and its venture with the UK post office.
The profit on disposal of the branch network is expected to amount to about 90 million after tax .