Duncan is a winner of the CableACE Award for Writing for a Dramatic Series for Vietnam War Story: The Last Days and a Christopher Award for Mr. Holland's Opus, which also garnered him a Golden Globe nomination. He was nominated for the Grand Jury Prize at the Sundance Film Festival for 84C MoPic and The Pornographer and the Independent Spirit Award for Best First Feature and Best Screenplay for 84C MoPic. He received the Vietnam Veterans of America Excellence in the Arts Award at the organization's 1989 National Convention in Chicago.