What Happened to Thomas Mark Harmon?
Mark Harmon, best known for his iconic role as Special Agent Leroy Jethro Gibbs on CBS's 'NCIS,' stepped back from his full-time acting role in the flagship series in 2021. Since then, he has remained an executive producer and narrator for the 'NCIS: Origins' prequel series and has co-authored a successful book series. As of 2026, Harmon is set to make a full-time on-screen return as Gibbs in the third season of 'NCIS: Origins'.
Quick Answer
Mark Harmon, the beloved actor known for playing Leroy Jethro Gibbs on 'NCIS,' departed from his full-time acting role in the main series in 2021 due to exhaustion from long work hours. He has since transitioned into an executive producer and narrator for the prequel series 'NCIS: Origins,' which explores Gibbs' early career. In a significant development for 2026, Harmon is slated to return full-time on-screen as the present-day Gibbs in all ten episodes of 'NCIS: Origins' Season 3, which premieres on October 6, 2026. Additionally, he has co-authored a series of historical non-fiction books, with 'Ghosts of Sicily' released in April 2026.
📊Key Facts
📅Complete Timeline13 events
Begins Acting Career
After a collegiate football career as a quarterback for UCLA, Mark Harmon began his acting career, often portraying law enforcement and medical personnel.
Joins 'St. Elsewhere'
Harmon gained significant recognition for his role as Dr. Robert Caldwell on the medical drama 'St. Elsewhere,' where his character's storyline included contracting HIV.
Named People's Sexiest Man Alive
Mark Harmon was named People magazine's Sexiest Man Alive, further cementing his status as a prominent Hollywood figure.
Marries Pam Dawber
Harmon married actress Pam Dawber, known for 'Mork & Mindy.' The couple has maintained a private life and has two sons.
Stars as Gibbs in 'NCIS'
Mark Harmon began his iconic role as Special Agent Leroy Jethro Gibbs in the CBS crime drama 'NCIS,' a character he first introduced in 'JAG.'
Wins People's Choice Award
Harmon received the People's Choice Award for Favorite TV Crime Drama Actor for his role in 'NCIS.'
Departs 'NCIS' as Regular Cast Member
Leroy Jethro Gibbs departs the main 'NCIS' series in Season 19, with Harmon stepping back from his full-time acting role due to long hours, though he remained an executive producer.
Co-authors 'Ghosts of Honolulu'
Harmon co-authored his first book, 'Ghosts of Honolulu: A Japanese Spy, A Japanese American Spy Hunter, and the Untold Story of Pearl Harbor,' with Leon Carroll Jr.
Appears in 'NCIS: Origins' Premiere
Harmon reprises his role as Gibbs, primarily as a narrator, and makes a cameo appearance in the two-part pilot episode of the 'NCIS' prequel series, 'NCIS: Origins.'
Guest Stars in 'NCIS'/'Origins' Crossover
Mark Harmon made a special guest appearance as Gibbs in a crossover event between 'NCIS' and 'NCIS: Origins' on Veterans Day.
Releases 'Ghosts of Sicily'
Harmon and Leon Carroll Jr. released their third book, 'Ghosts of Sicily: The True Story of the Naval Intelligence Agents Who Courted the Mob to Fight Nazis in America and Battlefields of Italy.'
Announced for Full-Time Return to 'NCIS: Origins' Season 3
It was announced that Mark Harmon will make a full-time on-screen return as the present-day Leroy Jethro Gibbs in all 10 episodes of 'NCIS: Origins' Season 3, with an arc tied to a present-day mystery.
'NCIS: Origins' Season 3 Premieres
The third season of 'NCIS: Origins,' featuring Mark Harmon's full-time on-screen return as Gibbs, is set to premiere on CBS.
🔍Deep Dive Analysis
Mark Harmon's career has spanned decades, but he is most recognized for his portrayal of Special Agent Leroy Jethro Gibbs on the highly successful CBS drama 'NCIS.' He originated the character in a two-part episode of 'JAG' in 2003, leading to the launch of 'NCIS' later that year. For nearly two decades, Harmon was the central figure of the series, earning multiple awards and nominations, including a People's Choice Award for Favorite TV Crime Drama Actor in 2017.
In October 2021, during the fourth episode of 'NCIS' Season 19, Harmon's character, Gibbs, decided to remain in Alaska, marking his departure as a regular cast member. Harmon later clarified that his decision to step back was largely due to exhaustion from the demanding 22-hour workdays during the show's early years and a desire for a better work-life balance. Despite his on-screen exit, Harmon remained an integral part of the 'NCIS' universe as an executive producer.
Following his departure from the main series, Harmon continued his involvement with the franchise by becoming an executive producer and narrator for the prequel series, 'NCIS: Origins,' which premiered in October 2024. The show explores a younger Gibbs' early days at Camp Pendleton in the 1990s, with Austin Stowell playing the younger version of the character. Harmon made brief cameo appearances in the series premiere in 2024 and a crossover event in November 2025.
A significant development occurred in June 2026, when it was announced that Mark Harmon would make a full-time on-screen return to the 'NCIS' universe in the 2026-27 season. He is set to appear as the present-day Leroy Jethro Gibbs in all ten episodes of 'NCIS: Origins' Season 3. This arc will involve a season-long mystery connected to Gibbs' past at Camp Pendleton, bridging the show's two timelines. The third season of 'NCIS: Origins' is scheduled to premiere on October 6, 2026.
Beyond his television work, Harmon has also ventured into writing. In 2023, he co-authored 'Ghosts of Honolulu: A Japanese Spy, A Japanese American Spy Hunter, and the Untold Story of Pearl Harbor' with retired NCIS Special Agent Leon Carroll Jr. They followed this with 'Ghosts of Panama' in 2024, and their third book, 'Ghosts of Sicily: The True Story of the Naval Intelligence Agents Who Courted the Mob to Fight Nazis in America and Battlefields of Italy,' was released on April 14, 2026.
What If...?
Explore alternate histories. What if Thomas Mark Harmon made different choices?