Parr wrote extensively for television animation. He wrote, and often story edited, for the Marvel series Spider-Man, G.I. Joe, The Transformers, Defenders of the Earth, Dino-Riders, and The Inhumanoids, as well as the pilot Pryde of the X-Men and the later X-Men series. Parr's other credits included The Smurfs, The Monchichis, The Get-Along Gang, Teenage Mutant Ninja Turtles, Heathcliff, Peter Pan and the Pirates, and Beetlejuice.