 Duncan debuted in vaudeville in 1906, after which he acted in stock theater companies in Memphis, Tennessee; Rochester, New York; and Philadelphia.He had a role in hundreds of serial episodes in a career spanning from 1911 to 1940, many of them Westerns.When William Duncan joined Vitagraph, his contract was worth $1,000,000 a year, which made him better paid than Mary Pickford and Douglas Fairbanks.