Nama, the Republic of Ireland's state-controlled "bad bank", has sold its entire NI property loan portfolio.
The buyer is an international investment firm, Cerberus Capital Management, based in New York.
It is understood they paid more than £1bn.
Nama's properties include office blocks, shopping developments, pubs and hotels and development land, and the Northern Ireland deal represents its largest single transaction.
Nama (National Asset Management Agency) was set up to handle property loans made by the Republic of Ireland's banks before the financial crash.
The Irish state broadcaster, RTÉ, reported the deal was for more than £1.3bn.
Nama had previously revealed that it paid around £1.1bn for the loans when it acquired them from the Irish banks.
However, as the loans originally had a value of £4.5bn, Irish taxpayers will still have lost out as ultimately they paid for the recapitalisation of the banks.
First Minister Peter Robinson said the sale was "excellent news for the Northern Ireland economy".
"For some time I have made clear the danger to the local economy of leaving valuable assets undeveloped and the threat that these posed to otherwise profitable businesses. I believe that this deal can be of real benefit to our economy," Mr Robinson said.
"I am grateful to the authorities in the Republic for the way in which this transaction has been handled and the importance of assisting the Northern Ireland economy."
The first minister said he had spoken to Nama chairman Frank Daly and former United States Vice President Dan Quayle of Cerberus Capital Management on Thursday evening.
He said the conversation with Cerberus provided "great encouragement that they will work with the developers and the executive to the benefit of all concerned".
"Dan Quayle offered to send a team to Belfast to meet with us to discuss the way forward and we intend to take him up on that offer.
"In the weeks to come the Northern Ireland Executive will work with Cerberus to ensure that the deal can help kick-start growth in this area of our economy."
Michael Noonan, the Irish finance minister, said: "Today's announcement by Nama of the sale of their Northern Ireland loan book to Cerberus is very good news for the Irish taxpayer, Nama and the Northern Irish economy.
"This is the biggest loan sale that Nama have completed to date and highlights the progress the agency is making in generating a return on its assets for the Irish taxpayer."
Sinn Féin's finance spokesperson, Pearse Doherty TD (member of Irish parliament), said he was concerned that Nama had not got the best price for the portfolio.
He said: "This policy of accelerated disposals seems reckless to me.
"A gigantic volume of loans and money has just transferred hands and the ball seems to have begun rolling on this only a couple of short months ago.
"Fire sales at the cusp of property price and economic recovery ring every alarm bell there is.
"While I support Nama's endeavours to dispose of loans effectively, I am concerned that, with six years to go until the agency's wind-up, they may be jumping that bit too soon at interested investors."