In 1971 Guardino starred in the short-lived series Monty Nash. Guardino had a continuing role as Perry Mason's nemesis, Hamilton Burger, in the 1973 television series The New Perry Mason and a recurring role on Angela Lansbury's Murder, She Wrote. He made guest appearances in dozens of television series, including Studio One, Target: The Corruptors!, The Eleventh Hour, Untouchables, Alfred Hitchcock Presents, Kraft Television Theatre, Playhouse 90, Dr. Kildare, The Lloyd Bridges Show, Route 66, Ben Casey, Hawaii Five-O, Twelve O'Clock High, Love, American Style, The Greatest Show on Earth, Kojak, The Streets of San Francisco, Jake and the Fatman, Cheers and The Untouchables with Robert Stack. He had the lead role of Det. Lee Gordon in the 1969 made-for-television suspense film The Lonely Profession.