Carey will replace Jennifer Lopez, who has exited the Idol stage as a judge along with Steven Tyler of Aerosmith, leaving just Randy Jackson as the sole remaining judge who has been with Idol since the beginning.
Fox execs are trying to spin the departure of Lopez and Tyler as a good thing, with Fox Entertainment President Kevin Reilly promising: "Change is going to be part of this show moving forward."
Carey is rumored to have agreed to a $17 million per year salary for serving as a judge on Idol, which saw its ratings drop by more than 20% last season.
Carey may be one of the bigger names to sign up as a judge for the show but some question that her heydey may have passed.
Sales of Carey's albums in recent years are just a fraction of what they once were.
Carey has largely avoided the spotlight since she became a mother in 2010. Her last album, "Memoirs of an Imperfect Angel," was released in 2009. She's wrapping up work on a new album and her stint on Idol is likely also fueled by promotional considerations for her new songs.
Idol isn't the only Fox show getting an overhaul as The X Factor is also getting a reboot as far as judges.
Britney Spears and Demi Lovato are taking over for Paula Abdul and Nicole Scherzinger, who were shown the door after just one season of serving as judges.
Idol may have slipped in ratings but it still remains one of Fox's most profitable shows and a cornerstone that much of its programming is built around each season.