As an adult, Marsh became a vice president of sales and marketing for a computer company. One day, he "freaked out" and decided to quit. A friend of his helped him put together a portfolio and go into the animation business. He eventually found himself working on the animated television series "The Simpsons" as a background layout artist in 1990. Marsh worked on the series for over six seasons and three episodes he helped produce won Emmy Awards. To help him with his animation efforts on the show, Marsh utilized several books about art, architecture design, and artistic rendering which he kept in his household library. His desk in the series' office placed him opposite of fellow layout artist Dan Povenmire; the two bonded over shared tastes in humor and music and quickly formed a friendship.