Through his publishing company Rowan, Rook and Decard, Howitt is a co-designer on Kieron Gillen's DIE: The Roleplaying Game.
Howitt began creating games in grade school, running downloaded PDF files through a text processor.
[3] Howitt began designing a new version of the Paranoia role-playing game with James Wallis and Paul Dean in 2014 for Mongoose Publishing.
[4] While living in Australia, Howitt designed his own role-playing game Goblin Quest, writing it on dozens of pages and spending weeks of work on it.
[1] Goblin Quest was 132 pages and he published it in 2015, and when he found this production schedule too difficult Hamilton suggested he start designing one-page role-playing games instead.
[1][12] In 2017, Howitt co-founded the games publishing company Rowan, Rook and Decard, with spouse Maz Hamilton as business director.
[13] Eat the Reich won three Gold ENNIE Awards in 2024 including "Best Cover," "Best Art – Interior," and "Best Adventure – Short Form."
[1] In a feature article on Grant Howitt, Chase Carter for Polygon called him "one of the foundational voices in the current generation of tabletop RPG creators"[1] because the success of Honey Heist inspired other designers to create and self-publish one-page games.
[22] In her PhD thesis, Susan Haarman wrote that Honey Heist by Howitt was one of the smaller independent games "that either minimize or eliminate combat altogether.
[23] Howitt has worked as a freelance writer for mainstream publications such as the Daily Mirror[24] and The Guardian[25] and indie organizations such as Video Brains.