Aer Lingus chief executive Stephen Kavanagh is to step down in January 2019 after four years in the role, but will remain on the airline's board as a non-executive director.
He will be succeeded as chief executive and executive director by Sean Doyle who is currently director of network, fleet and alliances at British Airways.
Mr Kavanagh has worked at Aer Lingus for the last 30 years, with the last four as chief executive.
He said he was stepping down to pursue other interests.
"By any objective measure Aer Lingus has been successful in recent years and continues to have significant opportunity to build upon the strong fundamentals of our value model. I'd like to thank all those who have provided support and guidance during my time in Aer Lingus," he said.
Willie Walsh, IAG chief executive and Aer Lingus chairman, said Mr Kavanagh has been an "exceptional" chief executive and has transformed and modernised Aer Lingus.
He also said that the company was delighted that Mr Kavanagh will remain on the Aer Lingus board and will provide "advice and guidance to the airline".
Mr Doyle, originally from Cork, joined British Airways in 2003. He has worked in financial, strategy, commercial and alliance roles at the airline.
Willie Walsh also confirmed that Aer Lingus chief operating officer Mike Rutter has extended his contract and will work with the new CEO to ensure that the airline continues to deliver its strong performance.