In 1976, Perrin published the Perrin Conventions, a set of alternative rules for Dungeons & Dragons combat.:83 Perrin was interested in getting more involved with the RPG industry, and with Jeff Pimper he talked with Chaosium about publishing a D&D-based monster manual, which they called All the World's Monsters (1977), which beat TSR's Monster Manual to market.:83 Perrin - along with Steve Henderson and Warren James - began working on an idea for an original gaming system for Glorantha, and were soon joined by Ray Turney from the original failed design team; this system was published as RuneQuest (1978).:83 Perrin officially joined Chaosium in 1981, although he just stayed a few years.:84 He was one of several authors who contributed to Thieves' World (1981).:85 Perrin's Worlds of Wonder (1982) was the third release under Chaosium's Basic Role-Playing system (BRP).:86Superworld, one of Worlds of Wonder's worlds, became its own game, although it was only moderately successful and Perrin later acknowledged that it was too similar to Hero Games' Champions.:87 Perrin's Elfquest (1984), based on the black and white Elfquest comic book, was another BRP release.:87 While at Chaosium he also created Stormbringer, and contributed to Call of Cthulhu. One of his first contributions to the world of RPGs was "The Perrin Conventions", a set of house rules for Dungeons & Dragons, which led to his work on RuneQuest.
Hero Games published its sixth RPG, Robot Warriors (1986), by Perrin.:147 He also wrote the 1987 Champions role playing game supplement The Voice of Doom.
Steve Perrin's Quest Rules (SPQR) is the latest Steve Perrin role-playing game, which he sells independently through Chaos Limited. In 2004 he collaborated with Taldren on Black 9 Ops as a paper and pencil accompaniment to the company's Black9 PC and XBoxgame, which fell afoul of developer-publisher friction and now looks to be unlikely to be published. Perrin decided to make Black 9 Ops available for free.
In 2010 Perrin began creating PDF adventures for the games "Icons" and "Mutants and Masterminds". He has completed several scenarios for Vigilance Press and Fainting Goat Press.