Why Is Mark Harmon Leaving 'NCIS' and Who is Taking Over? [DETAILS] "NCIS" will never be the same again because Mark Harmon is finally leaving the show after 18 years of portraying the lead role of Leroy Jethro Gibbs.
'NCIS' Season 18: Special Episodes to Be Aired Amid Mark Harmon Leaving the Show Rumors Is season 18 going to be the final season of "NCIS?" Last week's episode suggested that it's possible.
