Mark Bourke has announced he will step down as Chief Financial Officer of AIB early next year.
Mr Bourke joined the bank as CFO in April 2014 and joined its board the following month.
He was previously CEO of financial services company IFG.
The bank said a search for his successor will now start.
Mr Bourke is the latest senior banker to leave AIB. The bank has blamed its difficulty in retaining staff on a government pay cap.
AIB said last year it feared in particular losing staff to international banks that are moving operations to Dublin as a result of Brexit, and do not fall under the cap on executive pay and ban on bonuses that Dublin introduced a decade ago.
Of the bank's 200 most senior managers, a "mid-teens" percentage had left in the last year, chief executive Bernard Byrne said in July.
The bank sought to introduce a deferred share plan for senior executives earlier this year but it was voted down by the Government, which retains a 71% shareholding after a 2017 initial public offering.
While Finance Minister Paschal Donohoe acknowledged the restrictions could act as a barrier to the retention of some staff and launched a review of banking remuneration policy, he said the current policy remained appropriate.
AIB CEO Bernard Byrne said Mr Bourke's departure will be a big loss both to AIB and the bank's leadership team.
"He has contributed hugely to AIB's turnaround and our successful IPO. Mark has been a great partner to me and I wish him well in the next phase of his career," Mr Byrne added.
"I am extremely disappointed that Mark has decided to pursue his career outside of AIB. He has a great personal opportunity in his new role and he will leave with our best wishes," AIB chairman Richard Pym said in today's statement that did not say where Bourke was moving to.