Dunn was enrolled briefly at the University of Pennsylvania, but left after a short time to join a vaudeville troupe.

Dunn's Broadway credits included Once for the Asking (1963), Tenderloin (1960), Happy Town (1959), Make a Million (1958), The Pajama Game (1954), Room Service (1953), The Moon Is Blue (1951), An Enemy of the People (1950), and The Seventh Heart (1927).

[1] Dunn acted in hundreds of minor feature-film roles and supporting appearances in two-reel comedies.

He came to Hollywood during the early talkie era, beginning his film career with 1932's The Crowd Roars.

Dunn kept busy into the 1960s, appearing in TV series such as Kitty Foyle, The Edge of Night and Norby, and films such as Black Like Me.