According to Jeff Lenburg's assessment of him, King was an early pioneer of animation. His films were nominated three times for the Academy Award for Best Animated Short Film. He started his career in the silent film era. He spent most of his career working at Walt Disney Productions (later known as the Walt Disney Animation Studios). He directed many well-regarded films.
His film credits as an animator include several Silly Symphony animated shorts; which Lenburg describes as "cartoon fables". Among King's film credits was the film The Three Little Pigs (1933), which won the Academy Award for Best Animated Short Film.
Serving as one of Disney's key animation directors, he directed many classic Donald Duck cartoons (such as Donald's Dilemma) until his retirement in 1948. King directed more than 40 films featuring Donald Duck. Among them were the Academy-Award nominated Good Scouts (1938), Truant Officer Donald (1941), and Donald's Crime (1945). One of his films was a propaganda film, The Spirit of '43 (1943). It was created in association with the United States Department of the Treasury. King's last film was The Trial of Donald Duck (1948). Occasionally, he would also work as a sequence director for features, such as Pinocchio, The Three Caballeros, and The Adventures of Mr. Toad.