Jenny Ryan, best known for her role as a quizmaster on ITV show The Chase, left the show after the judges felt her performance wasn't strong enough.
But in a shock decision, the show announced via its Twitter account Jenny would be reinstated, joining Nicole Scherzinger's Overs category - which hosts acts over the age of 30.
The show's official account tweeted the announcement, stating: "The judges have decided that there is one person who still deserves a coveted spot in the X Factor Celebrity live shows.
"We're pleased to announce @jenlion will be joining @nicolescherzy in the Overs category this Saturday night!," it said.
The announcement follows a fan backlash, with #JusticeforJenny being used on social media as part of the campaign against the judge's decision.
One angry fan complimented Jenny on her "fantastic voice" and demanded two other contestants, Martin Bashir and Ricki Lake, should be sent home instead.
Another tweeted he is "banning the show from my household for the rest of my life unless Jenny is brought back."
He continued: "How can you put Martin through over Jenny. He as good but Jenny was the best on the show."
Another social media user claimed Jenny had been "robbed" of her chance to be in the talent show's live broadcasts.
The tweet questioned the judge's decision to put through "Ricki and Martin couldn’t even sing" and said Jenny should be put through as she was "incredible".
After learning of the decision to reinstate her, Jenny tweeted her surprise: "I was devastated that the judges didn't put me through, but the tidal wave of love & support I got from you all was incredibly uplifting, I am so grateful.
"I'm thrilled to have been thrown this lifeline, I won't let you down.
"See you at the Lives on Saturday!"
She followed up the tweet with a second, cheekily mocking the show, stating: "When the X Factor app updates you on your own life..."
Jenny is one of the acts taking part in the celebrity version of the show, which has well-known names compete on the stage instead of members of the public.
The show, now in its 15th year on British television, has had a make over in an attempt to quell falling viewing figures, having dropped an average of more than eight million viewers since its peak in 2011.