Dugan was born in Wheaton, Illinois, the second of four sons of Marion, a housewife, and Charles Dugan, an insurance salesman. He graduated from Goodman School of Drama at the Art Institute of Chicago (now at DePaul University) and started his acting career in 1969 in New York City. He moved to Hollywood in 1972 and appeared in his first TV show, "The Sixth Sense". Later, he played in the 1973 TV movie The Girl Most Likely to.... Other early film appearances include Night Call Nurses (1972), Night Moves (1975), Smile (1975), Harry and Walter Go to New York (1976) and Norman... Is That You? (1976). In 1979, he was cast as the time-displaced hero in Unidentified Flying Oddball, Disney's very loose adaptation of A Connecticut Yankee in King Arthur's Court. In 1981, he appeared in Joe Dante's adaptation of The Howling.