Monte Cook started working professionally in the game industry in 1988. In the employ of Iron Crown Enterprises, he worked with the Rolemaster and Champions games as an editor, developer, and designer. In 1994, Monte came to TSR, Inc., as a game designer and wrote for the Planescape and core D&D lines. When that company was purchased by Wizards of the Coast, he moved to the Seattle area and eventually became a senior game designer. At Wizards, he wrote the 3rd Edition Dungeon Master's Guide and served as codesigner of the new edition of the Dungeons & Dragons game. In 2001, he left Wizards to start his own design studio, Malhavoc Press, with his wife Sue. Although in his career he has worked on over 100 game titles, some of his other credits include Return to the Temple of Elemental Evil, The Book of Eldritch Might series, the d20 Call of Cthulhu Roleplaying Game, Book of Vile Darkness, Monte Cook’s Arcana Evolved and Ptolus. He was a longtime author of the Dungeoncraft column in Dungeon Magazine. In recent years, Monte has been recognized a number of times by game fans in the ENnies Awards, the Pen & Paper fan awards, the Nigel D. Findley Memorial Award, the Origins Awards, and more.
Monte launched a subscription-based dungeon crawl website in April 2009 at DungeonADay.com which hosts new content every weekday, eventually comprising an entire twenty-level dungeon.
On May 12, 2008, Paizo announced that they had hired Cook as rules consultant for their Pathfinder RPG, a revision of the 3.5 rules set that Monte helped design in 2000. In his blog, Monte confirmed that his role as consultant was minimal, but that he was actively involved in giving lead designer Jason Bulmahn feedback as he developed the Pathfinder RPG Alpha Release.