[1][2] Dunn began his career at the Walt Disney cartoon studio in 1951 as a inbetweener, where his first animation credit—Man in Space—received an Oscar nomination.
[3][2] He moved to Warner Bros. Cartoons in 1960; there, he began with The Pied Piper of Guadalupe, which was also nominated for an Oscar.
He and fellow Disney man David Detiege replaced Warner Brothers' top writers Michael Maltese and Warren Foster after they went to Hanna-Barbera to receive higher billing in the 1960s.
After the Warner's cartoon studio closed in 1963, Dunn joined DePatie–Freleng Enterprises; in 1964, he crafted the story for The Pink Phink, which earned the Oscar as Best Animated Short.
Dunn died in San Fernando, California of heart failure on 17 January 1983.