Gillespie began working for MGM in 1925, just a year after the founding of the studio; he remained on the job until 1962. His career with MGM was long enough so that he worked on the original 1925 silent version of Ben Hur, as well as the 1959 remake with Charlton Heston; and on the 1935 Mutiny on the Bounty, which starred Clark Gable, plus the 1962 remake with Marlon Brando.
Gillespie served as a set designer and art director, but made his reputation as an early special effects master. For most of his MGM career, Gillespie commanded a forty-man Prop Shop to realize his designs. Oddly, at MGM alone among the major Hollywood studios of its era, the special effects department was not an autonomous organization; instead, Gillespie reported to Cedric Gibbons, head of the Art Department.
The Wizard of Oz project provided unique challenges, such as making a tornado. The first effort, a 35-foot rubber cone, cost $8000 and did not work. Its replacement, a long muslin windsock double-sewn with music wire for strength, was better, and appears in the finished film. The tornado assaulted a miniature set of the Gale farm, with a three-foot-tall house and cornfields three inches high.
The deadly poppy field and the flying monkeys were among the other major effects realized by Gillespie and his team for the film. Others included Glinda's arrival in a pastel-colored bubble of light, and the phantasmagorical display of the Wizard of Oz's floating head in his throne room; the Wicked Witch's skywriting above the Emerald City, her crystal ball, and of course her dissolution with a bucket of water.
- Aljean Harmetz. The Making of The Wizard of Oz. New York, Delta edition, 1989.