TMDb/NCIS Celebrity NCIS's Timothy McGee is now the longest-serving cast member. A shocking episode reveals a secret 18-year-old romance, rewriting his personal history. March 19, 2026 AceShowbiz - Sean Murray's character Timothy McGee has been a staple of NCIS since its very first season in 2003, and now, more than two decades later, he stands as the longest-serving cast member in the 2025-2026 television cycle. Despite not being part of the original Leroy Jethro Gibbs MCRT team, McGee's journey has been deeply intertwined with the series' evolving storylines.