The No Country for Old Men duo have co-created HarveKarbo alongside Cedar Rapids writer Phil Johnston, according to Deadline.
The project will focus on a grouchy LA private detective who investigates the debauched lives of the Hollywood elite.
The Coens will executive produce alongside Johnston, plus Imagine TV's Brian Grazer and Francie Calfo.
The brothers are best known for their film work, including 1996's Fargo, 1998's The Big Lebowski, 2008's O Brother, Where Art Thou? and last year's True Grit.
Other comedy projects currently in development at Fox include a new pilot from the creators of How I Met Your Mother and a family sitcom from Cougar Town's Bill Lawrence.
A new project starring Arrested Development's Portia de Rossi and Shawn Levy's Gorilla Time are also in the works.
> Coen brothers to explore '60s folk scene with Inside Llewyn Davis