Chandler began his professional motocross career with the Maico factory racing team in 1979. He was nicknamed Magoo by his father at an early age, and the name stuck. By 1982 he had earned a place in the American Honda factory racing team. That same year he beat the vaunted Europeans at the 500cc U.S. Motocross Gran Prix at perhaps the toughest motocross tracks in the United States, Carlsbad. The victory would be the biggest of his career. In 1982 he also won both races in the Motocross des Nations as well as the Trophee des Nations, becoming the first rider to win both motos of both events in the same year.
After being dropped from the Honda team, Chandler went to Europe to compete in the Motocross World Championships. His career ended when he was left paralyzed after a crash at a supercross race in Paris. Despite the setback, Chandler began promoting mountain bike races and became involved with D.A.R.E. Chandler was inducted into the American Motorcyclist Association Motorcycle Hall of Fame in 1999.
Chandler died on May 4, 2010 from illnesses related to his paralysis.