Mark Harmon Drops a Bombshell About Gibbs’ Rules – Fans Won’t Be Happy

Mark Harmon spent nearly two decades bringing Leroy Jethro Gibbs to life on NCIS, and his iconic performance is a major reason the franchise has grown into the multi-series universe it is today.

Recently, NCIS: Origins – the prequel series exploring Gibbs’ early years – crossed over with the main show, giving fans something they’ve been hoping for: a rare return appearance from Harmon. It was his first time participating in the franchise since his 2021 exit.

A key focus of the crossover was one of Gibbs’ well-known Rules. Throughout NCIS, Gibbs developed a list of personal guidelines that became a signature element of the character. In this episode, the story revolved around Rule No. 11: “When the job’s over, walk away.” According to co-creator David J. North, Harmon recorded voiceover for the episode, and during their time in the studio, the topic of Gibbs’ Rules came up – something fans constantly want to talk about.

North explained that Harmon is approached by fans all the time asking about the Rules. But despite playing the character for so many years, Harmon doesn’t actually have them memorized. North said that when he asked Harmon whether he knew any of the Rules by heart, Harmon laughed and admitted he only remembered “the one about a knife.” That’s Rule No. 9: “Never go anywhere without a knife.”