Jackson had helped the 43-year-old 'Touch My Body' hitmaker to clinch the 18 million dollar deal with the show last year, reported Digitalspy.
Carey has signed a new deal with Red Light Management who look after Radiohead, Tim McGraw, Alicia Keys and Faith Hill.
Jackson started managing Carey back in 2011. He had also worked with her on a number of studio albums.
It has been reported that the entire judging panel on American Idol's current season will be dropped by producers in a bid to revamp the show.