A Montana native, Duncan has been working horses most of his life. Horses are what brought him to the notice of the film industry. A wrangler needed more horses for a film and Duncan was able to fill the need. Duncan's handiness with his training allowed him to be a valuable resource. With skills both in the saddle and at the end of driving lines, he has become a valuable asset on set. Duncan also has spent time with a wheel right and makes wagons. His craftsmanship extends also to saddle building. When meeting a director about wagons for a film, his charisma persuaded the director to offer Duncan his first acting part in the film "Steel Wind." Since then, he often appears in the films he brings his horses to as a stunt driver, stunt rider, and is cast as an actor.