There's no keeping any of Mark's family out of the entertainment business. Mark has been married to actress Pam Dawber since 1987. Known for her role as Mindy McConnell from the 1978 sitcom Mork & Mindy, Pam has a celebrated career in TV and film. She even guest-starred on NCIS with her husband for four episodes. She played Marcie Warren, an investigative journalist who grilled Gibbs on sensitive information during his suspension from active duty.

The long-married couple have two sons, one of whom also appeared on NCIS.

Eldest son Sean Harmon, who was born in 1988, followed in the footsteps of his parents and is also a professional actor. Alongside appearances in several dramas, he was also featured on NCIS as a young version of Gibbs in several flashback episodes.

Mark was especially proud of his son's performance as young Gibbs in the show's 400th episode, which aired in 2020.

"...I'm proud of him taking his work seriously and how he approaches being an actor," Mark stated in a 2020 interview with ET. "Not just on this show, just what he has chose to try to do with his life's work."

The couple's younger son, Ty Harmon, was born in 1992. He enjoys a showbiz career behind the scenes as a screenwriter.