The deal reunites the former American Idol judge with Simon Cowell, who will judge and executive-produce X Factor. Abdul, 48, and Cowell, 51, worked together on Idol for eight seasons before Abdul left in 2009. Cowell departed the next year to launch The X Factor in the U.S. after working on the original U.K. version for seven seasons.
"This show would never have been the same without Paula and I can't believe I am saying this - I have missed her a lot, and I am thrilled she's on the show," Cowell said in a statement.
"I am excited beyond words to be a part of The X Factor. I couldn't be happier to bring my love for cultivating talent and performance to such a wildly anticipated show," Abdul said. "I'm also delighted and grateful to be sitting next to Simon again...but you might want to check back with me in a week or two!"
The Emmy and Grammy winner joins previously announced judges Cheryl Cole, who worked on the British original, and former record label chairman Antonio "LA" Reid. Former Pussycat Dolls lead singer Nicole Scherzinger and British TV personality Steve Jones were announced as the hosts for X Factor on Saturday.
The announcement came on the heels of The X Factor's first audition taping, which took place Sunday in Los Angeles.
Following her exit from Idol, Abdul most recently judged and executive-produced the CBS dance competition series, Live to Dance.
The X Factor's winning act will receive a $5 million recording contract with Syco/Sony Music. The singing competition premieres in the fall on Fox.