Bord Gáis Energy managing director Dave Kirwan is leaving to take charge of customer operations at the Irish company's parent, Centrica, next month.
Mr Kirwan has led the natural gas and electricity supplier since mid-2011, bringing it through UK group Centrica’s takeover in 2014.
He is leaving the job to become Centrica’s managing director of customer operations in January, which gives him responsibility for more than 12,000 workers who handle more than nine million customers around Britain.
Mr Kirwan pointed out that the operation he would take over had “incredible scale” and said the appointment was a vote of confidence in Bord Gáis Energy and its staff on the part of its owner.
He noted that Centrica has been happy with the former Irish State company since buying it three years ago. “They realise that they got more than a business, they also got good people,” he said.
Mark Hodges, chief executive of Centrica Consumer, said that he was delighted to welcome Mr Kirwan.
"Dave is a highly experienced business leader who has demonstrated a strong customer-focused approach to the business in Ireland, " Mr Hodges added.
Mr Kirwan joined Bord Gáis in 1999 and worked in a series of senior management roles.
He was responsible for establishing its Northern Ireland subsidiary, Firmus Energy, and oversaw the construction and commissioning of its gas-fired electricity generators at Whitegate in Co Cork.
He began his career with another state company, ESB International, where he worked on building power plants in Texas and Vietnam.
A native of Tullow, Co Carlow, he qualified as an electronic engineer from University College Dublin before getting both a masters in business administration and then a doctorate in the economics of organisation and management from University College Cork.
Bord Gáis Energy will name Mr Kirwan’s successor next month.
