Atomic Kitten, Blue, Five, Liberty X, 911, Honeyz and B*Witched will release a cover Wizzard's 'I Wish It Could Be Christmas Everyday' on December 15 via Universal Music.
All profits from the song will go to ITV's Text Santa charity appeal, which raises money and awareness for six UK based charities in the run-up to a televised event on Friday, December 20.
Liz McClarnon from Atomic Kitten said: "When we started the talks for The Big Reunion this time last year, we couldn't have imagined we'd end up recording a Text Santa Christmas single! It's all for charity and we are so humbled to be a part of it!"
Keavy from B*Witched added: "Back in the day we were in competition with each other; this time round we get to do one big fantastic single together."
The cast's version of 'I Wish It Could Be Christmas Everyday' was produced by Cutfather (One Direction, The Saturdays) and will be the subject of a behind the scenes documentary that will air on ITV and ITV2.
Meanwhile, a second series of The Big Reunion is expected to air next year, with reports suggesting that Another Level and Eternal will appear.
Watch a trailer for The Big Reunion below: