Mark Harmon, renowned for his portrayal of Special Agent Leroy Jethro Gibbs on NCIS, has made significant strides in his post-acting career. After departing from the series in 2021, Harmon has remained involved as an executive producer and has ventured into new endeavors. In November 2023, he released his first historical nonfiction book, Ghosts of Honolulu: A Japanese Spy, a Japanese American Spy Hunter, and the Untold Story of Pearl Harbor, co-authored with former Special Agent Leon Carroll Jr. The book delves into the untold stories of Japanese-American intelligence officers during World War II .​

Harmon’s decision to leave NCIS was not influenced by health concerns, as previously speculated. In a statement, his representative clarified that reports citing his departure due to “failing health” were “completely false” . Instead, Harmon expressed a desire to explore new projects and spend more time with his family. He emphasized that he had not retired but was taking a step back to focus on other interests .​

While Harmon has not returned to acting, his continued involvement in the entertainment industry as an executive producer and author demonstrates his ongoing commitment to storytelling. Fans can look forward to his future projects, including potential collaborations within the NCIS franchise