Hackett became known to a wider audience when he appeared on television in the 1950s and '60s as a frequent guest on variety talk shows hosted by Jack Paar and Arthur Godfrey, telling brash, often off-color jokes, and mugging at the camera. Hackett was a frequent guest on both the Jack Paar and the Johnny Carson versions of "The Tonight Show". According to the board game "Trivial Pursuit", Hackett has the distinction of making the most guest appearances in the history of "The Tonight Show Starring Johnny Carson". During this time, he also appeared as a panelist and mystery guest on CBS-TV's "What's My Line?" and filled in as emcee for the game show "Treasure Hunt". He made fifteen guest appearances on NBC-TV's "The Perry Como Show" between 1955 and 1961. He appeared with his roommate Lenny Bruce on the "Patrice Munsel Show" (1957-1958), calling their comedy duo the "Not Ready for Prime Time Players," 20 years before the cast of "Saturday Night Live" used the same name.