From a very young age Sean was exposed to the world of acting, which he loved. Even though his parents were against him getting into the movie business, he knew that was what he wanted to do anyways.

Respecting their son's wishes, Sean's parents decided to do their best to help him start into acting. Sean's mother, Patty Duke, continuously received scripts from casting agents who were requesting her to star in various movies. She didn't even read most of the scripts at all because she knew that she wouldn't be interested in them. But when she got a script that called for a young boy as one of the lead roles she instantly knew that it would be the perfect way for Sean to start his acting career. So Patty spoke to her agent and they discussed the idea, then they proceeded to somewhat blackmail the production company so that Sean's could get the part. Patty told them that she would only take part in the movie if Sean could too, so that's exactly what happened.

Production of this film, called Please Don't Hit Me, Mom began when Sean was only nine years old. He was apparently a joy to work with and many of the crew members often spoiled Sean with candy and other small gifts, against Patty's wishes. Sean made a great first impression in many ways with this first film. He was well liked by the cast and crew, and Sean also displayed very promising talent in acting.

For the next few years it was somewhat difficult for Sean to get and good roles due to his lack of acting experience. But in early 1984, at the age of 13, he landed a plum role in The Goonies, an action-packed adventure film often described as an Indiana Jones movie for kids.

Sean learned a lot about special effects from this film. He also learned a lot from directors Richard Donner and Steven Spielberg (Spielberg wrote the story but only directed a second-unit crew). This prompted Sean to aspire to be a director, as well as an actor. He realized that as an actor, he could not implement his ideas into a film, since that was the director's job, which sounded very interesting to Sean.

Sean went on to star in a made-for-TV movie, The B.R.A.T. Patrol and then in White Water Summer with Kevin Bacon in 1987. Next came Like Father, Like Son which starred Kirk Cameron and Dudley Moore. This was Sean's first role in a teen comedy and helped him to gain status as a teen idol, apppearing in many magazines such as Teen Beat and other teen magazines, often with his brother Mackenzie. During these years, Sean also found time to attend the Crossroads High School for the Arts and he studied with the famous Stella Adler.

Sean proceeded to play a small role with Michael Douglas and Kathleen Turner in The War of the Roses in 1989. In the same year he starred with Dermot Mulroney for the first time in the family drama Staying Together. He would go on to star once again with Mulroney in the future.

In 1990, Sean was cast in his first adult role. He starred in the ensemble-cast film Memphis Belle with Matthew Modine, among others. The he starred in the little-seen horror film The Willies followed by Toy Soldiers, with Wil Wheaton, in 1991. The following year came Where the Day Takes You, in which he once again starred with Dermot Mulroney and the comedy Encino Man with Brendan Fraser and Pauly Shore. Also in 1992, Sean married a woman named Christine, who is three years older than he is. They were married on July 11,1992 at Sean's mother's house in Idaho, and they spent their honeymoon in Europe.

Next, Sean starred in one of his most critically acclaimed films to date. He played the title role in Rudy alongside Ned Beatty. This film proved his amazing acting talent once and for all. This led him into two movies in 1994. Safe Passage, with Susan Sarandon and Sam Sheppard and The Low Life, a small art house film. 1994 was also a huge year for Sean as he directed and co-produced with his wife Christine the short film Kangaroo Court which was nominated for an Oscar at the 67th Annual Academy Awards. Coincidentally, Sean's father was also nominated in the same category in 1969.

In 1995 Sean once again starred in a title role in the TV movie Harrison Bergeron. Although it was made for television, this film could have easily been a success in theaters, receiving rave reviews from many movie critics.

 1996 was a very important year for Sean. Not only did he have a small role in the spectacular film Courage Under Fire, but he also became a father. Sean and Christine had their first child, Alexandra Louise, on November 27th, 1996.

Sean now lives in Los Angeles with his wife and daughter, who are apparently very much "cat people", and because of this Sean actually got a kitten named Dusty to add to their family. Sean also continues with his ever-growing acting career. Over the past couple of years he narrated part of a Holocaust documentary entitled The Long Way Home, which won an Academy Award in 1998, and he also had a part in Warren Beatty's Bulworth. He also completed filming other movies including The Sky is Falling, Dish Dogs, and Boy Meets Girl, the last of which has seen limited release and may be available on video.  Sean is currently in New Zealand where he is filming the three Lord of the Rings films back to back.  Sean plays the important role of Samwise Gamgee in the trilogy.