Ulster Bank chief executive Cormac McCarthy is to step down from his post after 10 years.
Mr McCarthy (47) said in a statement he was leaving to seek "new opportunities" elsewhere.
“I have decided to move on from my position as chief executive of Ulster Bank as I believe that now is the right time for me to seek new opportunities,” he said.
A spokesman for Ulster Bank refused to comment further on reasons for the chief executive’s departure.
Mr McCarthy will remain head of Ulster Bank, which is owned by Royal Bank of Scotland, until his successor has been found. He will also stay on as deputy chief executive of Royal Bank of Scotland's UK retail unit until next year.
Mr McCarthy, who previously worked for First Active, took over as chief executive of Ulster Bank following its purchase of the former building society for €887 million in 2004.
Ulster Bank reported an operating loss of £137 million for the first quarter of 2010, following a £275 million loss in the final quarter of last year.
The bank said a rising number of mortgage customers were defaulting, due to cuts in the December budget and higher unemployment that impacted their ability to repay their loans.
The majority of Ulster Bank’s impairments came from its commercial property lending and other corporate loans.