She's been brought back to replace judge and former Spice Girl Mel B who is ill.
Tulisa previoulsy appeared on the ITV show until last year when she was dropped.
She'll mentor Italian Andrea Faustini who faces Ben Haenow and Fleur East in the decider of the singing contest.
Last month the N Dubz singer spoke about her Christian faith and said she was more religious than people know.
She told the Telegraph she's been going to the same church since she was young and prefers to go on her own.
"I wait until it is completely empty and light candles. The place I go to has 12 different icons, and I always go to Mother Mary, on the left-hand side, and I just sit there for half an hour and pray."
It was the first time the celebrity has spoken about her faith but she said that's because she had never been asked.
"I've never really talked about it because I know a lot of people aren't into it, and I don't want to bore...people. If they don't want to hear it, then there's no point trying to explain it," she said.
She admitted thinking speaking openly about her faith could damage her career, "It's like a personal thing," she said.