The 'Hero' singer was today announced by Fox to be joining the panel for the upcoming 12th season of the talent show next year
The announcement was made by Fox boss Kevin Reilly at the Television Critics Association's summer press tour in Beverly Hills today (July 23).
A telephone call between Carey and Reilly was played to the audience, in which she could be heard saying: "I am so excited to be joining Idol.
"I wanted to be there today and I wish I could have been there myself to tell you. I can't wait to get started in a couple months."
American Idol executive producer Nigel Lythgoe had earlier said: "I would like to see the judges change every year. It's horrible to be in this position where [the media] are asking, 'Who's it going to be?' and there are thousands of names being thrown out.
"And it's unfair on negotiations. You can't negotiate with somebody in a public marketplace."
Carey has previously appeared as a guest mentor on American Idol's seventh season, where contestants sang versions of her hits.
She was also at one stage lined up to join Simon Cowell as an advisor for The X Factor USA, but had to cancel her appearance due to Hurricane Irene.
The singer's appointment follows the departure of Jennifer Lopez and Steven Tyler after two seasons.
Meanwhile, her husband Nick Cannon hosts rival NBC show America's Got Talent, which will overlap with American Idol for a couple of weeks in May.
Cannon recently quipped that American Idol would not be able to afford employing his wife.
Mariah Carey will release her new single 'Triumphant ('Get Em)' in August.