He was one of the first writers hired for the series, as he had met co-creator Justin Roiland while working at 20th Century Fox Animation. McMahan described himself as "kind of the sci-fi guy" of the staff, and was promoted to showrunner for the show's fourth season, though he left during production to work on other projects.[3][4] In 2018, he won the Primetime Emmy Award for Outstanding Animated Program for his work as a supervising producer on the episode "Pickle Rick".[5]