Biological father is Michael Tell, who was married to Patty Duke for less than a month in 1970. Referring to both Tell and John Astin, Sean told the New York Daily News, "I consider both men my fathers, and have learned a great deal from each."
First professional acting job was at the age of 9, opposite his mother in the TV-movie Please Don't Hit Me, Mom.
Made his feature-film debut in the Steven Spielberg-produced The Goonies (1985).
Graduated cum laude from the University of California at Los Angeles.
In 2004, he published a memoir titled There and Back Again: An Actor's Tale.