The 38-year-old presenter also revealed that the veteran judge is desperate to improve the talent show following Simon Cowell's departure to the US version of the ITV format.
O'Leary told The Mirror: "Louis has got a new energy about him. There is a real sense of Louis being reborn in this panel.
"He is really obsessed with making it better. He really wants to beat Simon on the American show."
Meanwhile, O'Leary seemed to like Cowell's replacement on the panel, Gary Barlow, adding: "I think you can see Gary eased into the head judge's chair quite effortlessly. He has got quite an ambassadorial, almost presidential way about him."
> Gary Barlow: 'X Factor better without silly acts'
> X Factor Dermot O'Leary: Tulisa Contostavlos shouldn't be compared to Cheryl Cole'
Watch the X Factor judges chat to Digital Spy about the new series below: