The former Spice Girls star will join comic Howie Mandel and "shock jock" Howard Stern on the eighth series of the reality show, which is screened by NBC in the US.
NBC exec Paul Telegdy told Entertainment Weekly: "I've known Melanie since she did Dancing With The Stars... to know her is to know a very frank, strong, enduring entertainer. Someone who has a very strong point of view.
"We needed somebody who was qualified for the job. She's an amazing singer, dancer and a huge personality. The contestants will get a lot of constructive feedback from her, and I can't wait to see her chemistry with Howard and Howie."
We told you recently that Mel had reportedly ruled out a job on The X Factor UK - although it was claimed that she was targeting the Aussie version of the show.
Meanwhile Sharon Osbourne is reportedly being lined-up for a return to The X Factor in the UK.
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