Barr appeared several times with Dean Martin (his nephew) and Jerry Lewis when they hosted the Colgate Comedy Hour.

However, in the wings of the stage just before the comic's entrance, he has a brief conversation with Johnny Hooker (Robert Redford), who addresses him as "Leonard".

Barr's comedic schtick was one-liners; told with a straight face, and sometimes deliberately repeating a punchline.

He is perhaps best remembered internationally for his appearance in the 1971 James Bond film Diamonds Are Forever with Sean Connery in which he played Shady Tree, a stand-up comedian and smuggler in Las Vegas who was assassinated by henchmen Mr. Wint and Mr. Kidd.

Cameron Crowe briefly depicted Barr as a foul-mouthed real-life character in Almost Famous, his semi-autobiographical film of 2000.