The stars, along with George Clooney's girlfriend Stacy Keibler and Kelly Osbourne, have been linked to the posts in recent weeks, and on Tuesday (16Oct12) the co-presenters were confirmed.
In a post on her Twitter.com page, the reality TV star writes, "The rumors are true... I will be hosting TheXFactorUsa this season!!! So excited!"
She later took to her blog and added, "I'm a huge fan of the show, so I literally fell over in my chair when I heard that I was being considered for the role.
"The show already has such an incredible panel of judges and it is truly an honor to have been given this opportunity to work with them. I'm thrilled, overjoyed and of course a little nervous about this new step in my career, and I can't wait to get started. Wish me luck!"
Lopez adds, "Looking forward to working with SimonCowell and the rest of the amazing team."
Britney Spears, who features as a judge on the show alongside Simon Cowell, L.A. Reid and Demi Lovato, declared, "Welcome to TheXFactorUsa team, KhloeKardashian and MarioLopezExtra - so excited to have you as co-hosts!"
The stars replace Welsh presenter Steve Jones, who was fired from the series after the first season.
The second season of the talent show debuted last month (Sep12) with a series of audition episodes, while the live programmes are set to be broadcast from 1 November (12).