Lisburn has beaten Dublin for almost 1,000 John Lewis jobs with the opening for the first time in Ireland of the up-market British department store.
The company's board had considered Tallaght as a site but decided to build at Sprucefield, outside the Co Antrim city.
Work is expected to begin next year once planning has been approved. An announcement confirming the huge investment is due tomorrow.
Apart from the store, it is understood the company will also build all its warehousing for Ireland at Sprucefield. A second shop may open in the Republic later.
Upper Bann Democratic Unionist MP Jeffrey Donaldson, who met with representatives of the John Lewis board a fortnight ago, said be believed the development could put the brakes on the numbers of shoppers from Northern Ireland travelling to Dublin.
He said: "We hope that this will reverse the trend - significantly."