From an early age, Gilroy loved comic books and animation which inspired him to study film at several colleges in the greater Los Angeles area.

[1] It was at Warner Bros. that Gilroy sold his first script to the producers of the Emmy winning Batman: The Animated Series, for the Scarecrow episode, "Nothing to Fear".

Joe: Renegades and Kaijudo, and then moved on to Marvel Animation Studios where he acted as supervising producer and head writer on Hulk and the Agents of S.M.A.S.H.

Gilroy is co-creator of the first Bionicle trilogy and has since written for numerous other animated series, such as The Mask, Justice League Unlimited, The 99, Kim Possible, and the direct-to-video Disney movie title Atlantis: Milo's Return and the Funimation anime film Mass Effect: Paragon Lost based on the hit video game for Electronic Arts and BioWare.

[7] In 2014, Gilroy returned to Lucasfilm under Disney studios to serve as co-executive producer and series writer of Star Wars: Rebels where he wrote seventeen episodes through 2018.