Leona, who was a guest judge on Saturday, and Rita, who joined the panel yesterday, will take it in turns to judge auditions at the O2 Arena.
Rita will join Gary Barlow, Louis Walsh and Tulisa again in the morning, while Leona will be on the panel in the evening.
“I am really excited to be a guest judge at the auditions in London," former X Factor winner Leona said this week. “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.”
Breakthrough singer Rita meanwhile reassured the hopefuls that she was only starting out herself.
Tweeting yesterday before her first stint as a guest judge, Rita wrote: "IM HERE...... I CANT BREATHE! X-FACTOR..... IM JUST LIKE YOU REMEMBER THAT. IVE JUST STARTED TOO IM HERE TO HELP!"
The X Factor will air in the autumn on ITV1.