Bank of Ireland (BoI) has agreed to invest €175m in a tie-up with the Post Office in Britain that will give it access to 29 million customers.
A new range of financial products developed and sourced by BoI will be sold from early next year through the Post Office's 16,900 branches - one of the largest retail network's in Europe.
The product range will include personal loans, savings accounts, credit cards, personal insurance and mortgages; and will carry the Post Office brand.
The joint venture will be owned equally by the Post Office and the bank and has an initial term of ten years.
BofI has an exiting relationship with the Post Office through First Rate Travel Services, a foreign exchange business which generated over €50 million in profits last year.
Mr Mike Soden, BoI chief executive said the 176 million investment in the UK market was central to the bank's strategy.
"This joint venture, combined with our existing personal and business banking operations in the UK, gives Bank of Ireland a unique level of access to the UK retail financial services market.
"It's the beginning of a new chapter for Bank of Ireland in the UK market," Mr Soden said.
Mr David Mills, Post Office chief executive, said BoI had fought off intense competition to secure the contract. "We selected Bank of Ireland because of its ability to deliver products that will appeal to our customers and because of our existing highly successful relationship.
He said BoI's expertise allied with the Post Office's extensive branch network - greater than every bank and building society in Britain combined - had created "a business with very exciting potential".
The agreement is subject to final contracts being signed and regulatory approval.