The new ITV show is based on a US series hosted by Jerry Seinfeld and sees a celebrity panel trying to resolve a married couple's arguments.
Jo Brand was originally thought to be in the running for the role but O'Leary has now signed a deal to front the programme.
"It's a great show and the kind of thing I want to present because it's not your usual show," O'Leary said. "It's something I'd watch. I'd never do a gameshow. ITV have big plans for it, so fingers crossed."
Stars due to appear on the programme include Brand, Jack Dee and Sarah Millican.
Celebrities who have taken part in the show in the US include Madonna, Bette Midler and Demi Moore.
Filming for the seven-part series is expected to begin next month and the show will air later this year.