The deal, which gained Competition Authority approval both here and in Britain in late October, will see the ESB strengthen its leading share of the all-Ireland electricity market, which was merged three years ago.
The acquisition will also result in the ESB taking control of a number of NIE subsidiaries, including NIE Powerteam Ltd and Powerteam Electrical Services (UK) Ltd, which provide electrical construction and maintenance services.
The NIE business employs approximately 1,300 staff.
The Bahrain-based investment bank, Arcapita will keep ownership of the Viridian Group, which it acquired in 2006, and which will now focus on its electricity and gas generation and supply businesses and its other remaining subsidiaries; Power Procurement and NIE Energy Supply — which, combined, employ around 340 people.
While the deal had previously attracted objections from Unionist leaders in the North its successful completion is broadly on schedule.
ESB chief executive, Padraig McManus, said his management team was delighted with the acquisition of “an efficient and successful company”.
He said the ESB is “committed to making the capital investment required to match future growth in the economy and to meet the Northern Ireland Government’s targets in relation to the development of renewable energy”.
Viridian chairman, Patrick Haren, added: “Under Viridian’s ownership, NIE has strengthened its network capacity and improved, significantly, its service delivery to customers. Under its new owners, it will meet the challenge of grid development and delivering increasing volumes of renewable energy to customers.”