Aer Lingus says its outgoing CEO Christoph Mueller will now leave his role on 28 February - and not in May as previously announced.
The airline said its chairman Colm Barrington would take executive responsibility for strategic matters with immediate effect.
He would take full executive responsibility for the group from the start of March, Aer Lingus said in a statement to the stock exchange, until a new CEO had been appointed.
Aer Lingus was subject to an informal takeover approach by International Airlines Group, owner of British Airways and Iberia, late last month.
Mr Mueller’s decision to leave Aer Lingus was first announced by the airline in July 2014.
He is due to take up the role of CEO at Malaysia Airlines, which was renationalised last year after losing two aircraft in separate incidents.