He made his first movie, Sunshine, in 1973 at the age of 12. His first regular starring role was as younger brother Jack on The Fitzpatricks. Michele Tobin played his sister, Mo, on the show, and they later worked together on California Fever. McNichol sang the show's theme song, and in 1978 recorded an album with his sister, Kristy, produced by Phil & Mitch Margo.