The Square's matriarch and former landlady of The Queen Vic will return to Walford later this year when she learns that her eldest son Phil needs his mother's help.
Barbara's return as Peggy will be part of a roller-coaster storyline during the autumn, which is set to be dramatic for the Mitchells. Viewers will see Phil landing himself in trouble, Roxy planning to get hitched to Alfie and the return of Samantha Womack as Ronnie Mitchell.
"It is no secret how much I have always loved EastEnders and Peggy Mitchell," said Barbara. "And by the number of times I'm constantly stopped by the great British public and asked either, 'When are you coming back?' or please say, 'Get out of my pub', it seems they have too!
"It may only be a short visit, but it's a family matter and as Peggy always said: 'It's all about family.'"
Executive producer Lorraine Newman, added: "We're delighted to announce Barbara's return for a very special episode. Peggy's surprise visit is a wonderful treat for our fans, as well as the cast and crew here on EastEnders. It's great to welcome her home."
Peggy Mitchell has been a memorable character in the long-running BBC1 soap and some of her most famous storylines include her battle with breast cancer, her famous slap with Pat Evans and her marriages to Frank Butcher and evil Archie Mitchell.
Barbara, who played Peggy for 16 years, left the soap in 2010. Her exit storyline saw Peggy leave Walford for Portugal in a bid to help Phil turn his life around.
Watch Peggy's 2010 exit in the soap below: