The hit US reality television show will debut on the digital channel in the same week it launches on Fox in the US.
"American Idol is immense. We believe it's going to be a defining show for 5* building on an already impressive schedule," said Channel 5 head of acquisitions Katie Keenan.
"American Idol is one of the world's biggest and most established entertainment brands," added senior vice president of sales Justin Hatfield.
"The series has won over audiences globally with its mix of top talent, performances and superstar judging panel. We look forward to working with 5* on what promises to be another smash hit series."
The show has been airing on ITV2 since 2002.
American Idol season 12 will debut in January 2013 with host Ryan Seacrest and judges Mariah Carey, Randy Jackson, Nicki Minaj and Keith Urban.