He is the youngest of four children (he has two older step-brothers, Rick and Mark, and an older step-sister, Ana). His mother's name is Linda. His father, Myles Marsden, a choreographer, founded the Rhode Island State Ballet. As such, as a small child, Jason was surrounded by dancers and actors. Friends of his parents suggested he get an agent and do some acting work in commercials.

At the age of eleven, Jason had moved from Rhode Island to California and had his first major role, as the third child to play Alan Quartermaine Jr. in the long running American soap opera, General Hospital. He continued this role for two years, whilst still attending elementary school. This was followed soon afterwards by the role of Eddie Munster in the TV series remake of "The Munsters" titled The Munsters Today. At the same time as doing The Munsters Today, Jason also had his first voice acting role in a cartoon, that of Cavin in the Disney cartoon TV series The Gummi Bears.

Jason continued with small acting and voice-acting roles in sitcoms, cartoons, and films until 1992, where he landed the role of Dash X in Eerie, Indiana. This is notable because it is most often the role that people will associate with the name Jason Marsden. While the program only ran for 19 episodes, and Jason only appeared for 6 of them, the program gathered a cult following and is still enjoyed today.

Although starring in a TV film, providing voices for cartoons, and guest-starring in sitcoms, Jason's next memorable role was a voice-acting one, that of Goofy's son, Max Goof, in the animated film A Goofy Movie (1995). A prominent role in White Squall (1996) closely followed this, where Jason had the opportunity of working with the famous director Ridley Scott and actors Jeff Bridges, Ryan Phillippe, and Ethan Embry. Another role that made him a household name was that of Rich Halke in Step by Step, which was from 1996 until the show's cancellation.

Since Step by Step, Jason has provided voices for numerous animated television shows and computer games, appeared in a straight-to-video film, been the voice of Kovu in The Lion King II: Simba's Pride, the voice of Haku in the American dub of Sen to Chihiro no kamikakushi (more commonly known as Spirited Away) (2001), starred in two TV films, and has made guest appearances on some of the most popular American sitcoms out there. His most noticeable recent TV appearance is playing the young Burt Ward/Robin in the 2003 TV Movie Return to the Batcave: The Misadventures of Adam and Burt.

Jason has a passion for acting and would like to direct. He has already made his first foray into directing, an episode of The Journey of Allen Strange (1997). He is known for his boyish good looks, talent for physical and vocal comedy, multi-faceted acting skills, and lack of height (being 5'3" tall).

In recent years he is probably best known for his voice over work on the various DC Warner Bros animated series such as Justice League, Static Shock, Teen Titans, Batman Beyond and The Batman.

His best man at his wedding was his best friend and actor, Will Friedle (most famous in recent years for playing Terry McGinnis/Batman in Batman Beyond). Coincidentally the two have worked together in the series in a couple of episodes.

His hobbies are ice-skating, rollerblading, drawing, swimming, and collecting Disney videos.

Being a huge Walt Disney fan his pets are named Aladdin, Jasmine and Lady.

He is currently the head annoucer for Toon Disney and also serves as a part-tme annoucer for Disney Channel.