Guardino's other film credits include Houseboat, Pork Chop Hill (about the Korean War), The Five Pennies, King of Kings, Madigan, Lovers and Other Strangers, Dirty Harry and The Enforcer. He was nominated twice for the Golden Globe Award for Best Supporting Actor. He guest starred on John Cassavetes's 1959–1960 series, Johnny Staccato, the story of a pianist/private detective in New York City.
In 1960, Guardino appeared as Johnny Caldwell in the episodes "Perilous Passage", "The O'Mara's Ladies", and "Daughter of the Sioux" in the NBC western series Overland Trail starring william Bendix and Doug McClure. McClure two years later would join the long-running The Virginian series on NBC after a preceding stint on the CBS detective series Checkmate.
In 1964, he was cast in a CBS series entitled The Reporter, a drama about a hard-hitting investigative Journalist named Danny Taylor. His principal co-star was Gary Merrill as city Editor Lou Sheldon. He had co-starred with Merrill the year before in "The Human Factor" episode of The Outer Limits.
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.
In 1993, a Golden Palm Star on the Palm Springs, California, Walk of Stars was dedicated to him.
Guardino died of lung cancer in Palm Springs, California in 1995.
