Mark Harmon was born in Burbank, California to Tom Harmon, a University of Michigan football All-America and Heisman Trophy and actor and artist, Elyse Knox. Mark has two older sisters, actress and painter Kristin Nelson, the former wife of singer Ricky Nelson, and actress Kelly Harmon, who was once married to car magnate John DeLorean.
He first attended Los Angeles Pierce College as a student and quarterback and then transferred to University of California, Los Angeles. He was the starting quarterback for the UCLA Bruins in 1972 and 1973. He graduated from UCLA with a B.A. in Communication in 1974.
He started working in commercials for Kellogg's Product 19 cereal and became a longtime spokesperson. He then appeared in an episode of "Ozzie's Girls" and got recurring roles on "Adam-12" and "Emergency!" in mid-1975. He was later cast in "Sam", about an LAPD officer and his K-9 partner in 1978. In 1979, he starred in the action series "240-Robert" as Deputy Dwayne Thibideaux.
His first big role was on the soap opera, "Flamingo Road", where he played Morgan Fairchild's husband Fielding Carlisle. He next landed the role as Dr. Robert Caldwell "St. Elsewhere" in 1983. In the mid-80's, Harmon was also the spokesperson for Coors Beer.
He played Ted Bundy in the 1986 television movie The "Deliberate Stranger". He also worked on the series, "Moonlighting", playing Sam Crawford for four episodes in 1987. He also played the Chicago police detective Dickie Cobb for two seasons from 1991-1993 on the series "Reasonable Doubts". In 2002, he had a short run playing Secret Service Special Agent Simon Donovan on The West Wing. Mark then took a lead role in JAG in April 2003, which introduced him as Agent Gibbs which we would later see on "NCIS". Since then, Mark has starred as Leroy Jethro Gibbs in NCIS.
He loves carpentry and has shown his skills on "NCIS" throughout the seasons. He has been married to Pam Dawber since March 21, 1987. They have two sons, Sean Thomas Harmon and Ty Christian Harmon.