Yes — but only once, and only briefly.
Mark Harmon’s Leroy Jethro Gibbs shows up during the NCIS Season 6 backdoor pilot episodes, “Legend” Parts 1 & 2, which introduce the future NCIS: Los Angeles team. In these episodes, Gibbs visits the Office of Special Projects and interacts with Callen, Sam, Kensi, and Hetty.
After the spin-off launched, Gibbs never appeared on NCIS: LA again, but his cameo helped establish the connection between the two shows and officially welcomed the new team into the NCIS universe.
