A spokesperson for the show this morning confirmed reports that the young singer will join Gary Barlow, Louis Walsh and Tulia.
At 21, Rita will be one of the youngest judges to ever sit on the panel, and with only one single, the pressure is on.
Sources have claimed that X Factor boss Simon Cowell hopes that Rita will be able to become the show's new full time judge from bootcamp in August.
"It’s hers to lose. If she does well as a guest judge on Monday, she’s got a real chance of getting the job," an insider told the Daily Star Sunday today. “Bosses have been hugely impressed by her in meetings and they feel she has an amazing future.
“She’s the girl of the moment – and she’s incredibly sexy.”
Auditions will be taking place at the O2 Arena, where former X Factor champ Leona Lewis joined the panel yesterday.
She said: “I am really excited to be a guest judge at the auditions in London.
“The X Factor is where it all started for me and now I’m back... and sitting on the other side! I think London has a lot to offer.
“I’m looking forward to seeing the talent. It’s going to be a fun day working alongside the other judges.”