In 1983, Prady was a production assistant for The Jim Henson Company on a proposed television special centering on the world of technology. When the project failed to come to fruition, he stayed with the company and worked in the merchandising department. With the encouragement of Jim Henson, he began writing on projects including Fraggle Rock: The Animated Series and The Jim Henson Hour (on which he was visually caricatured as the character Chip). In 1991, he received an Emmy-award nomination for co-writing The Muppets Celebrate Jim Henson. He wrote the Disney theme park attractions Muppet*Vision 3D and Honey, I Shrunk the Audience.
In 1995, Prady joined the writing staff of the HBO series Dream On. In 1997, he joined the writing staff of Dharma & Greg, rising to executive producer and taking over as showrunner in 2001. He also served as a writer and producer on Good Morning, Miami, Caroline in the City, Related, Platypus Man and Gilmore Girls.
In 2007, Prady co-created the CBS sitcom , on which he served as executive producer for the show's twelve-season run.