Television
In the 1953–54 season, O'Hanlon appeared several times on NBC's The Dennis Day Show. In 1957, he played Charlie Appleby on an I Love Lucy episode, "Lucy and Superman". O’Hanlon played a character listed as “Caldwell” in a 1958 episode of Maverick, entitled “Rope of Cards”, S1 E17. In 1958, O'Hanlon played a New York publicist for a fashion model in How to Marry a Millionaire.
In 1960, he originally auditioned for the role of Fred Flintstone for the Hanna-Barbera Productions animated series The Flintstones, but lost the role to Alan Reed.
In 1962–63, he voiced one of his most prominent characters, George Jetson in the original The Jetsons, a role he would reprise over 20 years later in two additional seasons from 1985 to 1987.
In the autumn of 1964, he appeared as a cab driver in the 13-episode CBS drama The Reporter. In 1966, O'Hanlon appeared opposite Jackie Gleason as Ralph Kramden's loudmouthed "bum brother-in-law", on Gleason's first TV show of the 1966-67 season. He also made various appearances on ABC's Love, American Style, a series for which he wrote the teleplays and also directed several episodes.
In 1971, O'Hanlon appeared as a bear trainer on The Partridge Family, season 2, episode 6, "Whatever Happened to Moby Dick?", a drunk, who was jailed with Oscar and Felix in a memorable episode of The Odd Couple, season 2, episode 6, "Murray the Fink," and a drunk in Adam-12, season 4 episode 1, "Extortion".
