Manetti's signature role on Magnum, P.I. lasted for the entire eight-year run of the series (1980–88). He also had co-starring roles in 25 feature films and guest starred on many other television shows, including Rockford Files, Emergency!, Tenspeed and Brownshoe, Fantasy Island , Battlestar Galactica, Renegade, Quantum Leap, JAG and Walker, Texas Ranger. Manetti also had a minor role in the 1993 film CIA II: Target Alexa.