The country's rail boss is leaving for a job in Australia.
In the midst of a pay dispute with Irish Rail drivers and the company in difficult financial circumstances, David Franks is to move to a new public transport role overseas in the coming months.
He held the post of chief executive for five years.
Frank Allen, Iarnrod Eireann chairman, said: "I want to thank David for his immense contribution to Iarnrod Eireann over the past five years.
"David has led Iarnrod Eireann at a very challenging time for the company and has delivered significant improvements in safety, passenger growth of 24% and new customer-focused systems and processes.
"These changes will benefit the company for many years to come."
Mr Allen said the outgoing chief executive will remain fully committed to addressing challenges at the company as he sees out his notice.
Mr Franks joined Iarnrod Eireann in 2013. He previously worked for Keolis UK, a division of the French national railway company SNCF.
The announcement of his departure follows warnings from unions on Wednesday of industrial action as drivers fight for a wage increase as part of commitments to train new staff.