King began his career writing the television movie Imaginary Friends in 1983. He wrote the science fiction horror film The Nest in 1988 and action sequel Silk 2 in 1989. He co-wrote the horror film Eric's Revenge in 1989. He wrote the romantic comedy Under the Boardwalk and the martial arts film Bloodfist also in 1989.

He continued to write feature films throughout the 1990s. Full Contact (1993) and Dragon Fire (1993) were based on King's script for Bloodfist. He wrote the comedy Clean Slate and romantic comedy Speechless in 1994. He co-wrote the 1995 film Cutthroat Island. He wrote the political thriller Red Corner in 1997. He wrote and directed the comedy film Principal Takes a Holiday in 1998. He co-wrote and directed the 2000 television movie Angels in the Infield. He also co-wrote and produced the action movie Vertical Limit in 2000.

King and his wife Michelle co-created the short-lived drama series In Justice in 2006. The series aired as a mid-season replacement on ABC. As well as the pilot King co-wrote the episode "Golden Boy". The series was not renewed after completing a thirteen episode first season.

The Kings co-created a second legal drama series entitled The Good Wife. They served as executive producers for the series. As well as the pilot episode they co-wrote the episodes "Stripped", "Unorthodox" and "Hi". King and the writing staff were nominated for a Writers Guild of America Award for Best New Series for The Good Wife.