As a young man, MacDonald landed a job as a musician on the Dollar Steam Ship Lines, which in 1934 led to an opportunity to record music for a Disney cartoon.

In addition to directing sounds for animated shorts as aurally complicated as Mickey's Trailer (1938), he developed many original inventions and contraptions to achieve expressive sounds for characters like Casey Jr., the circus train engine from Dumbo (1941); Evinrude the dragonfly from The Rescuers (1977); the bees in Winnie the Pooh and the Honey Tree (1966); and Buzz-buzz (later called "Spike"), the bee who gets the best of Donald Duck in his 1950s short films.

He also made the sound effects of Tick Tock the crocodile from Peter Pan (1953) and Dragon Maleficent from Sleeping Beauty (1959) by using castanets.

By the time of his death, he was preparing to work on the sounds for the Splash Mountain attraction in Tokyo Disneyland and Walt Disney World.

[5] Despite formally retiring, MacDonald remained involved with several Disney productions; he voiced Evinrude from The Rescuers (1977) and was often consulted for sound-effects projects.