In 1983, he received a congressional appointment to the United States Merchant Marine Academy at Kings Point, New York.
In 1987, he graduated with a Bachelor of Science degree in marine transportation and an officer's appointment in the United States Maritime Service.
He was in more than ten movies including The Deadly Trackers, The New Adventures of Heidi and the Disney animated short film The Small One, but he is most commonly known for playing the protagonist Pete in the 1977 Disney movie Pete's Dragon for which he earned a gold record.
Marshall was a guest star in many of the popular series of his time including Kung Fu, Emergency!, Code R, The Carol Burnett Show and Tony Orlando and Dawn to name a few.
Marshall was also a prolific TV commercial, radio, print and stage actor during seven years in the entertainment industry.