The Hollywood Reporter said Fox Entertainment President Kevin Reilly made the announcement Monday during a press conference in Los Angeles.
"We do, in fact, have one judge whose deal closed very recently," Reilly said. "It's an artist that many contestants have tried to emulate. Because it really was concluded only hours ago, our new judge couldn't be with us."
"I am so excited to be joining 'Idol,'" Carey told reporters by speakerphone. "I can't wait to get started."
Randy Jackson said last week on "The View" he would be back again as judge on Season 12 of "Idol." There is no word on who the third judge might be.