He started out in animation screenwriting in the mid 1980s, cutting his teeth on the Disney movies The Fox and the Hound, The Black Cauldron, The Little Mermaid and Oliver and Company and shows such as Challenge of the GoBots. By the late 1980s he had become a staff writer for Walt Disney Television Animation, working on many of the well-known Disney cartoons from that era. He served as an episode Writer Co-Producer, Voice Director and Story Editor for The New Adventures of Winnie-the-Pooh, in which his personal writing style of subtle humor and underlying intelligence became apparent. In 1989, in order to fill a major gap in Disney's production schedule, he co-developed a new series with fellow staff writer Jymn Magon called TaleSpin, for which they ironed out the concept in only three days. They both oversaw the expedited production of the show, which went from a rough draft concept to completed episodes in less than a year. The show became the first new series created for the newly formed Disney Afternoon. He left Disney around 1992. Shortly after, he developed a cartoon series for Film Roman based on the Mighty Max line of toys, aptly named Mighty Max. This series is a great example of the characteristics that defined his career: stories driven by three-dimensional characters, intelligent dialog chock-full of hidden yet relevant references, and zany situations. He also helped develop the ABC Saturday morning cartoon Cro in 1993. He reunited with Jymn Magon in 1994 for Superhuman Samurai Syber-Squad. Other notable series co-developed by Zaslove include Bump in the Night and The Legend of Calamity Jane. Mark Zaslove was an credited crew member (along with Roque Ballesteros, Lyla Warren, Jeff Biancalana, Alan Lau, Warren Graff and Kenn Navarro) on Space Jam, Quest for Camelot and The Iron Giant. He met Roque, Lyla, Jeff, Alan, Warren and Kenn again as he was working on the ultroviolent Happy Tree Friends. In 1998, Palisades Films optioned feature rights to Zaslove's script Sincerely Maggie based on the life of singer/songwriter Maggie Louie but the film was never produced. Zaslove jumped into the international scene in the 2000s, serving as a story consultant and show writer for the children's series LazyTown, produced in Iceland. He also became heavily involved in the emerging entertainment industry in India as well as making his foray into live-action writing and directing. He is a two-time Emmy award winner and a recipient of the Humanitas Prize.