Following weeks of speculation, Fox's entertainment president Kevin Reilly made the announcement at the Fox executive session panel at the Television Critic's Association Summer Press Tour.
"I'm so excited to be joining 'Idol.' I wanted to be there today and I wish I could've been there myself to tell you," Carey told the audience via phone after Reilly called her and put her on speaker.
"It happened really quickly. I can't wait to get started in a couple months. Everybody have a great TCA and I will see you in January."
Reilly would not confirm any other rumors, including whether or not Randy Jackson will be back in judging capacity.
"We finished the show at the top again -- Phil Phillips went to gold faster than any other 'Idol' in the history of the show -- but our ratings were down," Reilly said. "Not being the only game in town now we needed to keep things fresh.
We had a dialogue with everyone on the bench. We have the biggest names in the business interested in doing the job. It’s going to be a matter of finding the right chemistry and making a deal.
Randy has been working with Mariah for a long, long time. Randy was instrumental in doing this deal."
Shortly after the announcement to the audience, Fox issued a statement confirming Carey's "Idol" involvement.
