Mark Harmon’s influence on the set of NCIS has long been a topic of fan speculation, and now several cast members have confirmed exactly what viewers suspected. Harmon wasn’t just the lead actor—he was the quiet, steady force that held the team together. Castmates described him as professional, grounded, and deeply committed to making the set a positive environment.

Sean Murray, who plays McGee, has spoken about Harmon’s leadership as being crucial to the show’s success, saying the longevity of NCIS wouldn’t have been possible without him. Others echoed the sentiment, pointing out that Harmon led by example, never drawing attention to himself but always setting a tone of respect and discipline.

Behind the scenes, Harmon helped build a culture of camaraderie and consistency. He made an effort to know every crew member by name, kept the vibe on set focused, and stepped up to support new actors when they joined. Whether it was offering advice, giving space, or simply listening, Harmon made people feel valued.

For many in the cast, working with Harmon wasn’t just a job—it was a masterclass in humility and professionalism. Their respect for him is clear, and it’s now evident that the lasting chemistry on-screen was rooted in a real, unshakable trust off-screen.