Cowell, who also produces the show, said in a statement, "It's taken more than a decade but I'm delighted to finally be on a panel with three girls (I think!).
"Paulina and Kelly both have great taste and massive experience in the music industry and, together with Demi, this is going to be a fun panel. It just feels like the time to do something different."
Rowland already has some judging experience, as she held the position on the British version of the reality talent show. She says, "I am very excited to be reuniting with Simon Cowell and The X Factor family. It feels great to be able to take this journey here at home in the states!"