The cable channel has ordered a script for the half-hour comedy pilot, says The Hollywood Reporter. O'Brien's Conaco and Warner Horizon Television will develop the project.
Fat Chance centres on two best friends - an overweight individual named Chance and his handsome friend. The show takes a look at what happens to their friendship when a beautiful girl enters their lives.
Last year, O'Brien signed a deal with TBS to host his own talkshow after leaving NBC.
The TV personality has called his Tonight Show sacking "a very human situation". He also said that his closing remarks during his final Tonight Shows helped him form a bond with his audience.
He explained: "I felt I could be honest with people… I think some of the stuff that I talked about on the last Tonight Show resonated with people and it was honest, and I felt like, 'All right, let's keep going with this. Let's just keep trying to let people in'."
Watch Conan O'Brien's surprise visit with Jimmy Fallon below: