Born in Brooklyn in 1924, Hackett became interested in show business while in high school. He toured the Borscht Belt, working in various capacities, prior to serving three years in the army during World War II. After leaving the service, he studied acting in New York and began working as an actor and comedian there and in California. An appearance in the 1954 Broadway production Lunactics and Lovers helped him land a role in the short-lived live TV comedy series Stanley. He later replaced Art Carney on The Jackie Gleason Show and made regular appearances on The Tonight Show with Jack Paar.
In addition to his other Broadway appearances in Viva Madison Avenue!, I Had a Ball, and Eddie Fisher and Buddy Hackett at the Palace, Hackett is well known for his roles in such films as The Music Man, It's a Mad, Mad, Mad, Mad World, and The Love Bug. He provided the voice of Scuttle in Disney's The Little Mermaid and reprised that role for the direct-to-video release The Little Mermaid II: Return to the Sea, his final film credit.
Hackett is survived by his wife, Sherry Cohen, and three children.