BORD Gais Energy has appointed John Barry as acting chief executive.
Mr Barry, who has been managing director of Bord Gais Networks since 2008, will take the reins after John Mullins ended his term as CEO yesterday.
In a statement, the company said it was in the process of recruiting a new chief executive and it expected to make an appointment early this year.
As well as his role at the head of Bord Gais Networks, Mr Barry is currently the programme director for the establishment of Irish Water.
Bord Gais Energy chairman Rose Hynes said: "I wish to thank John Mullins for his exceptional contribution to BGE over the past five years as CEO.
"Under his stewardship, the company has been transformed and has seen significant growth. I wish John every success in the future," she added.
Mr Mullins had indicated he planned to step down earlier this year, but it wasn't until June that it was confirmed he would be going at the end of his current contract.
Mr Mullins has taken a series of cuts to his pay package in recent years. In 2010, his salary was €399,000, which dropped to €343,000.
Now, the salary for his position has been capped at €250,000.
Despite the success of Mr Mullins as chief executive – the company has been transformed as it moved into an open market – he was known to feel the end of this year would be a natural break point.
Bord Gais has won the contract to take over the water utility, and it was likely the cost of setting up that business and the installation of controversial water meters would be an undertaking that would need a long-term boss in place at the head of the company.
He has previously indicated his desire to work in the private sector once he finished his time with Bord Gais Energy.