The New Jersey native's[citation needed] early career was spent on television in series such as Bonanza, Room 222, Alias Smith and Jones, Mannix, Emergency!

Dunn's breakout role was as the judge (and Barbra Streisand's character's father) in the 1972 film What's Up, Doc?, for which he was noticed by Mel Brooks, who was in the process of forming a stock company of actors.

He also appeared in several Walt Disney productions, such as The World's Greatest Athlete (1973), Charley and the Angel (1973), Herbie Rides Again (1974) and Gus (1976).

[citation needed] Additional television credits include Twigs, All in the Family, Barney Miller, McMillan & Wife, Rhoda, Sanford and Son, and The Mary Tyler Moore Show, S4Ep6.

Additional film credits included roles in Catch-22 (1970), The Great Northfield Minnesota Raid (1972), A Reflection of Fear (1972), Emperor of the North Pole (1973), Papillon (1973), Killer Bees (1974), Bank Shot (1974), At Long Last Love (1975), The Night That Panicked America (1975), Peeper (1976) and High Velocity (1976).