The pop superstar and former programme finalists are both tipped to appear on the results episode on Sunday, November 13.
Host Dermot O'Leary confirmed yesterday that JLS will perform on Sunday, November 6.
Florence + the Machine, who released second album Ceremonials today, will join the X Factor boyband on the upcoming results show.
Frontwoman Florence Welch this week told Digital Spy of the performance: "I've only seen a couple of episodes this series but I'm really enjoying it.
"It would be a real experience to perform on that show. I'm one of those people that is up for most things... I'd definitely be keen to step into that world and explore it without getting too involved."
GaGa appeared on The X Factor in 2009 to perform her single 'Bad Romance'. Watch the performance below: