Sean's full name is Sean Patrick Duke. He was born on February 25, 1971 in Santa Monica, California. His parents are John Astin and Patty Duke. He has one brother, and four half-brothers. Their names are: Mackenzie Astin (brother), born 1973; David Astin; Allan J. Astin, born 1961; Thomas E. Astin, born 1965; and Kevin Michael Pearce.

He was married to actress/producer Christine Harrell in July of 1992. He has two daughters: Alexandra Louise Astin, born November 27, 1996; and Elizabeth Louise Astin, born August 6, 2002.

Sean's film debut was as Michael 'Mikey' Walsh in The Goonies. He is currently working as a director (when he can) as well as an actor. His other roles have been: Sam Gamgee in The Lord of the Rings, Rudy Ruettiger in Rudy, William 'Billy' Tepper in Toy Soldiers, and many others.

He currently lives in Los Angeles with his family.