POWER NI's parent company Viridian has been bought by American investment group I Squared Capital for an estimated €1 billion (£785m).
The company, which also owns Energia in the Republic, is Ireland's largest independent integrated energy firm.
The firm was offered for sale by its Bahraini owners Arcapita which had bought the group for £1.6bn in 2006.
Arcapita filed for Chapter 11 protection in the US in 2012 after talks with creditors over a syndicated loan failed.
However, it exited bankruptcy a year later after securing a US$350m (£234m) loan from Goldman Sachs.
Viridian has around 480 workers and has a 20 per cent of domestic electricity and 27 per centre business electricity sales across Ireland.
It has a generation portfolio consisting of 747 megawatts of gas-fired combined-cycle generating technology capacity and 225MW of onshore wind assets in operation and construction.
the company also has 793MW of operating wind-farms under long-term contracts which is expected to increase to around 1,000MW in just over a year.
I Squared Capital partner Gautam Bhandari said the acquisition was "consistent with our strategy of investing in robust growth economies, such as Ireland, and within those economies selecting companies with stable cash flows and a potential to grow the business organically and through bolt-on acquisitions".
Viridian CEO Ian Thom said he was "excited by the opportunity to work with I Squared Capital, which brings a proven track record of successfully operating and helping to expand businesses such as Viridian".
The acquisition is expected to complete in the second quarter of the year.
I Squared Capital said it had also paid down around £145 million in existing junior debt with new equity at closing which it said would strengthen Viridian’s capital position and support future growth potential.
