Salem, who was born and raised in Los Angeles, is a 1973 graduate, of Agoura High School, in Agoura, California.

He has appeared in over 80 guest starring roles on television, including Francis Campion in Testimony of Two Men (1977), Marcel Pasquinel in Centennial (1978), and the ghost of a dead soldier in an Emmy Award-winning episode of M*A*S*H. His film roles include the role of Jocko in Triumph of the Spirit (1989), the role of The Grand Inquistor in Ridley's Scott's 1492: Conquest of Paradise (1992), and the bleach blonde French gangster in Roger Avary's Killing Zoe (1994).

In 1991, Salem won a Drama Log award for his performance in Richard Greenberg's "The Extra Man" at South Coast Repertory Theater, as well as a Boston Critic's award for his performance as "Cousins" in George Bernard Shaw's Major Barbara with Cherry Jones at the American Repertory Theater in Cambridge. Salem also co-starred on Broadway as "Scoop" in The Heidi Chronicles with Mary McDonnel.

In 1997, Salem earned an Emmy Award as a Writer for the television special Don King: Only in America, which also earned him a PEN nomination. The film also won the Broadcast Film Critics Award and Peabody Award for Best Television Film of the year. He received a second Emmy nomination the following year for writing The Rat Pack, in addition to a second PEN nomination. Also, as Brad Stephens in Hawaii Five-O season 8 episode, "The Deadly Persuasion".

In 2018, Salem was hired by Warner Bros./DC Films to write the screenplay for the upcoming comic-based movie Jack Kirby's New Gods, directed by Ava DuVernay.