Since 2003, Harmon has starred as former U.S. Marine Corps gunnery sergeant and sniper turned NCIS Special Agent Leroy Jethro Gibbs in the hit CBS series, NCIS, a role that has become Harmon's best-known role to date while also giving him international recognition.
His first role came about thanks to his sister Kristin's in-laws, Ozzie and Harriet Nelson. His role in Ozzie's Girls led to other roles, including guest spots on Adam-12 and Emergency!, which were executive produced by Dragnet star Jack Webb.
In 1980, Harmon played his first prominent role as Morgan Fairchild's husband on Flamingo Road. Shortly after the series was canceled, Harmon was cast as Dr. Robert Caldwell on St. Elsewhere.
After three years, he left the show in 1986. In 1987, he made four guest appearances on Moonlighting as Cybill Shepard's romantic interest.
From 1991-1993 he played Det. Dicky Cobb on TV's Reasonable Doubts. There were 44 episodes.
In 1996, Harmon played another doctor, Jack McNeil, on Chicago Hope. He remained on the show until 2000. In 2002, he had a minor supporting role as a Secret Service Agent on The West Wing which ended when his character was killed off.
In 2001, Harmon starred in the TV movie, "And Never Let Her Go", playing Thomas Capano alongside British-born Canadian actor, David Hewlett (Dr. Rodney McKay in the Stargate TV series).
Two years later in April 2003, Harmon appeared in what would become his recurring and most famous role to date: former Marine Gunnery Sergeant/NCIS Special Agent Leroy Jethro Gibbs. Harmon along with actors Michael Weatherly, Pauley Perrette and David McCallum along with Robyn Lively made their respective debut appearances in the JAG season 8 episodes, "Ice Queen" and "Meltdown", both of which served as backdoor pilots for NCIS with the main NCIS series premiering five months later on September 23rd, 2003.
In addition to his television credits, he has also appeared in a number of feature films, including Beyond the Posiedon Adventure (1979), the lead role in Summer School (1987), The Presidio (1988) with Sean Connery, Stealing Home (1988) with Jodie Foster, the 2003 remake of Freaky Friday, and he played the president of the United States in Chasing Liberty (2004).
Born in Burbank, California, Harmon is the son of Heisman Trophy winner Tom Harmon and actress Elyse Knox. He has two older sisters, Kristin and Kelly, who were married, respectively, to singer Ricky Nelson and car magnate John DeLorean. Harmon's niece, Tracy Nelson, is also an actress.
Harmon is married to actress Pam Dawber, who is famous for playing Mindy McConnell, opposite the late Robin Williams as Mork, on the 1970s sitcom Mork & Mindy.
Their son, Sean Harmon has made occasional appearances on NCIS as a younger Gibbs in flashbacks.
Before becoming an actor, Harmon worked as a carpenter. These skills are alluded to by Gibbs's habit of building boats in his basement.
Harmon was voted People magazine's Sexiest Man Alive in 1986.
- From Season 6 of NCIS onwards, Harmon became a Producer on NCIS and in Season 9, was promoted to Executive Producer for NCIS. In addition, Harmon currently serves as an Executive Producer for NCIS: New Orleans, the spin-off series of the main NCIS series.
- Attended the Los Angeles Pierce College which actor Paul Schrier also attended.