High Quality Content by WIKIPEDIA articles! Magnum, P.I. is an American action drama television series starring Tom Selleck as Thomas Magnum, a private investigator in Hawaii. The series ran on CBS, which broadcast 162 first-run episodes over eight seasons, from December 11, 1980, to May 8, 1988, plus two crossover episodes that aired as episodes of other series (Simon & Simon and Murder, She Wrote).