The Associated British Foods-owned chain has bought the 120 Littlewoods stores for £409m, although the deal excludes the home shopping activities.
Both Asda and Tesco had been linked as potential bidders for Littlewoods since it came on the market in January. Now the two supermarket giants can only hope to pick up some of the stores to be sold off to ABF.
Littlewoods stores trade from a total of 2.1 m sq ft and ABF said it intended to sell 60% of the current retail space. It will convert the prime sites to Primark stores, to build onto the 122 outlets currently in the portfolio.
In the half-year to March 5, Primark reported a sales increase of 12% to £448m and an operating profit increase of 18% to £59m. Like-for-like sales were up 6%.
George Weston, Chief Executive of Associated British Foods, said: "This is a unique opportunity to acquire a portfolio of large stores in attractive high street locations. It will bring Primark to many towns and cities where it is currently not present."