“With sadness in my heart, I’ve decided not to return” to the hit Fox TV singing contest, Abdul said in a posting on her Twitter account.
In a statement, Fox said she was a “tremendous talent” and wished her all the best.
Fox announced that Kara DioGuardi would return for a second season on the American Idol judging panel that includes Simon Cowell and Randy Jackson.
The addition of Grammy-nominated songwriter DioGuardi last year raised questions about Abdul’s future.
In July, Abdul told The Associated Press that she had been invited to stay with Idol as long as the show lasted and that she was optimistic that she would be able to negotiate a new contract.