Jonathan Tweet started playing D&D in the 1970s, when his father gave him his first Dungeons & Dragons game. He briefly played with a group of college students, although he says, "but the DM killed me off... because he didn't want a twelve-year-old in his group". Tweet then formed his own gaming group by recruiting classmates.
Jonathan Tweet and Mark Rein•Hagen founded Lion Rampant in 1987, while students at Saint Olaf College where they also met Lisa Stevens who later joined the company.:232 His article "Egyptian Magic for Call of Cthulhu” appeared in Different Worlds #47 (Fall 1987), the magazine's final issue.:84 In 1987, Tweet and Rein•Hagen designed the game Ars Magica, a game centered around wizards in the Middle Ages.:232–233 Tweet left Lion Rampant and the RPG industry in 1989 to start a new career.:234 Tweet wrote Festival of the Damned (1991), an adventure published by Atlas Games for Ars Magica.:252 Tweet continued to run a game for a group in Rock Island, Illinois, and wrote about the game "Al Amarja" in Alarums & Excursions; when John Nephew saw these A&E articles he wanted to publish the game, and the result was Over the Edge (1992), the first original game from Atlas Games.:253 His design on Over the Edge notably involved free-form rules and a subjective approach. Lisa Stevens suggested that Tweet revise the Talislanta rules for Wizards of the Coast and write its first new adventure; this resulted in a revision of the Talislanta Guidebook (1992), which was soon followed by his adventure The Scent of the Beast (1992).:277 Tweet wrote the adventure Apocalypse (1993) for Mayfair Games' Role Aids line.:169 Nephew and Tweet also designed On the Edge (1994), a collectible card game based on Over the Edge.:253 Tweet became a full-time employee of Wizards of the Coast in June 1994, and heralded in new lines from Wizards, the first of which was Ars Magica, recently acquired at Tweet's suggestion.:279 Tweet designed Everway, which was first published by Wizards of the Coast in 1995.:254, 280 After Wizards of the Coast moved away from role-playing games, Tweet worked on Portal, a Magic: the Gathering set designed to help new players learn the game.