Mark Harmon’s return to the NCIS universe is already sending shockwaves behind the scenes, with insiders claiming cast and crew members are preparing for a high-pressure season as the longtime franchise star steps back into the spotlight.

Harmon, 74, famously played Leroy Jethro Gibbs for more than 18 seasons on NCIS before stepping away from the hit CBS drama. At the time, he made it clear he was ready to move on. But now, his comeback is being viewed as a major sign that the franchise may be entering a critical new chapter.

According to an insider, Harmon’s return is not just about nostalgia.

“Mark officially retired and said he wouldn’t be coming back, so the fact that he’s doing this says a lot about where his head is at,” the source said. “It isn’t about having fun or taking another victory lap. He’s coming back because he feels a real responsibility to get the franchise back on track.”

The comeback comes as NCIS has reportedly faced a sharp ratings slide. The series averaged 7.85 million viewers during its 2024-2025 season, down by 9.7 million viewers from the previous year. After years as CBS’ most-watched scripted series, NCIS also reportedly lost that title to Tracker, the network’s action-drama starring Justin Hartley.

Now, Harmon is expected to play an older version of Gibbs in every episode of the third season of NCIS: Origins this fall. He is also said to have appeared in several crossover episodes with the original NCIS in November 2025.

NCIS: Origins stars Austin Stowell as the younger version of Gibbs, while Harmon has served as narrator and executive producer on the prequel series.

While many connected to the show are reportedly grateful that Harmon is returning, sources claim his comeback is also creating tension because of the intense standards he is known for bringing to a set.

“Everyone is grateful that Mark is coming out of retirement to help because they know what a huge boost this is for the show, but there’s also a lot of anxiety because nobody expects him to take it easy,” one source said.

The insider added that Harmon may have a calm public image, but behind the scenes, he is said to be intensely focused.

“He may come across as this quiet, laid-back guy, but behind the scenes he’s incredibly driven and expects the same level of commitment from everyone around him,” the source claimed.

Harmon’s influence on the show goes beyond his role as Gibbs. As an executive producer, he reportedly holds significant authority over the direction of the series, which has only added to the pressure on the cast and crew.

“That means there’s a ton of pressure to impress him, and with Mark, there’s no room for coasting,” the source said.

Another insider claimed Harmon is expected to demand the same discipline from everyone around him that he demands from himself.

“He expects 110 percent from everyone on the cast and crew, and if anyone isn’t pulling their weight, they’ll hear about it,” the source said.

Still, the source insisted the actor is not viewed as unreasonable.

“It’s not a case of him being unfair,” the insider explained. “He pushes himself just as hard. It’s just that his standards are sky-high.”

For many fans, Harmon’s return will be welcome news. Gibbs remains one of the most beloved characters in the NCIS franchise, and his presence could give NCIS: Origins a major boost as producers look to keep the long-running universe alive and competitive.

But behind the scenes, insiders say the mood is a mix of excitement and nerves.

“Everyone knows he’s back to steady the ship, not make friends,” the source said. “So people are definitely sweating.”