Les Clark was born in Ogden, Utah in 1907, the eldest of 12 children to James Clark, a carpenter, and Lute Wadsworth. By 1910, the family lived in Salt Lake City and by 1920, they lived in Twin Falls, Idaho. By 1930, they lived in Los Angeles, where he attended Venice High School. During high school, he worked a summer job at an ice cream shop near Walt Disney Studios in Hollywood. Walt and Roy Disney were frequent patrons at the shop, and Walt had once complimented Les on his lettering job of the menus. Eventually, Les got the courage to ask Walt for a job. He recalled Walt's reply:
Les started work at the studio first as a camera operator and doing ink and paint on the animations. He moved on to work under the guidance of Ub Iwerks. During the development of the character Mickey Mouse, Clark was promoted to the position of 'inbetweener' where he worked on a scene for the upcoming Steamboat Willie. Les was then promoted to Animator and was tasked with the iconic scene The Skeleton Dance in Silly Symphony. After Ub Iwerks left Disney, Clark was given the position as lead animator on Mickey Mouse. He continued honing his craft, attending art classes while working at the studio. As he improved, he was given the task of animating The Seven Dwarfs in the upcoming film Snow White and the Seven Dwarfs, in particular, the scene where Snow White dances with each of the seven dwarfs. He would go on to animate the iconic Disney characters Pinocchio, Cinderella, Alice and Tinkerbell.