The actress will start filming in January after three years away from the BBC One primetime soap.
Viewers last saw Stacey flee the country with her baby daughter Lily, after Janine Butcher exposed her as the killer of Archie Mitchell.
Lacey's portrayal of the loud-mouthed and opinionated Stacey created one of EastEnders' most-loved characters and won her more than 30 awards for her role.
Her work acting out Stacey's bi-polar disorder won her plenty of praise, as well as Stacey's affair with her father-in law, Max Branning.
Lacey said: "I may have left EastEnders over three years ago, but the show has always been in my heart - as has Stacey - and she has never really left my side.
"I am so excited about returning and seeing what the future holds for her. It's been a while since I set foot in Albert Square and I am looking forward to coming home."
Exact details of Stacey's comeback storyline are yet to be revealed but show bosses have promised that her return will "send ripples of drama" through Albert Square.
Executive producer Dominic Treadwell-Collins added: "Stacey is one of EastEnders' best-loved characters, played by one of television's finest actors, and I am tremendously excited that Lacey has decided to return home to Walford.
"Stacey's last time on The Square was iconic. But that was just the first act. There is so much more to come for Stacey and her return will send ripples of drama through The Square."
Since leaving EastEnders in 2010, Lacey went on to star in numerous dramas including Being Human, Switch and BBC One's Our Girl. Lacey will also be filming a five part series of Our Girl next year.
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Check out one of Stacey's most memorable moments in the video below: