Kilroot power station near Carrickfergus, which had been facing closure, has been given a new one-year deal to provide energy to the grid.
Its owners, AES, said the move would "ensure energy stability" for NI.
It means around 170 jobs will be saved, but 85 posts are likely to go at its sister station at Ballylumford outside Islandmagee.
Business organisation Manufacturing NI said the deal will add costs to consumer bills.
The agreement was hammered out following negotiations between AES, the Utility Regulator and the operator of the grid, SONI.
AES said the deal "shows the importance of the facilities we are operating".
But it added a "re-structuring" of its business would have consequences for jobs and negotiations would now start with trade unions.
In January, AES had said it wanted to close Kilroot after failure to win a contract to supply the all-island single electricity market.
AES had also applied for permission from the Utility Regulator to close part of Ballylumford.
In a statement following the deal, SONI said security of supply would have been risked by allowing the shutdown of generators at both plants.
The initial contracts were awarded after auctions intended to increase competition and lower prices.
Manufacturing NI said by now giving AES a new deal, consumers would be left to shoulder "£14m of additional cost".
Its chief executive, Stephen Kelly, said he was "really disappointed."
The utility regulator said the average annual household bill will rise by £6.
Ulster Unionist MLA Roy Beggs welcomed the move as "good for the stability of our electricity supply".
Kilroot is one of Northern Ireland's main power plants and uses coal-fired generation.
It was always likely to face closure within the next three or four years as coal-burning technology would fail to meet environmental standards.