Roleplaying

Cook has been a professional game designer since 1988, working primarily on role-playing games. Much of his early work was for Iron Crown Enterprises as an editor and writer for the Rolemaster and Champions lines. Cook worked for Iron Crown Enterprises for four years; two as a freelancer and two as a full-time designer. During this period, he attracted fan and critical attention with the popular multi-genre setting Dark Space.

Cook began working for TSR in 1992 as a freelancer, "writing a whole slew of stuff for the old Marvel game that never came out because the game got canceled". Joining the TSR team, Cook designed Dungeons & Dragons modules such as Labyrinth of Madness (1995) and A Paladin in Hell (1998), and dozens of supplements to the Planescape line including the Planewalker's Handbook (1996) and Dead Gods (1998). Cook also designed the conspiracy game Dark?Matter (1999). After TSR was purchased by Wizards of the Coast, Cook became a Senior Designer, and was part of the team working on the D&D game's third edition. Cook, Jonathan Tweet, and Skip Williams all contributed to the 3rd edition Players Handbook, Dungeon Master's Guide, and Monster Manual, and then each designer wrote one of the books based on those contributions. Cook was proud of the work he did on the new Dungeon Master's Guide, especially after Gary Gygax gave his comments to the team as feedback on the book: "He said that the material in the new DMG would help him become a better DM... That was really cool—and satisfying in a 'completion of the circle' sort of way." Cook said in 2000 of his involvement with Wizards of the Coast and Dungeons & Dragons, "It's a great time to be working here... because every product is big, important, and innovative."

Cook left Wizards of the Coast in 2001 and started Malhavoc Press to write material for the d20 System independently. Malhavoc's first product, The Book of Eldritch Might, is widely credited with demonstrating the viability of PDF publishing within the role-playing industry. Notable work under the Malhavoc banner includes Arcana Unearthed, a product he describes as a "variant Player's Handbook". He also wrote or co-wrote a few more products for Wizards of the Coast as a freelancer, including the d20 version of Call of Cthulhu.

Fiction

Cook graduated from the 1999 Clarion West writer's workshop, and has published the novels The Glass Prison and Of Aged Angels. He has also published short stories like "Born in Secrets" (in Amazing Stories), "The Rose Window" (in Realms of Mystery), and "A Narrowed Gaze" (in Realms of the Arcane). He also writes a continuing Call of Cthulhu fiction series, "The Shandler Chronicles," in Game Trade Magazine.

Malhavoc released Ptolus, a campaign setting based on Monte Cook's home game, in August 2006. Ptolus was also the playtest campaign for the third edition designers. The book was unusually large and expensive for a roleplaying game supplement, being 672 pages and costing over $120 US.

Shortly after the release of Ptolus, which Cook has often described as the culmination of his original ambitions for Malhavoc, he announced that he would be focusing on writing fiction and other forms of creative work for the foreseeable future. White Wolf and Goodman Games announced his final RPG books. Monte Cook's World of Darkness, his own take on White Wolf's modern horror setting, was released at Gen Con 2007. From Goodman Games is Dungeon Crawl Classics: #50, "Vault of the Iron Overlord", which was also targeted for the same Gen Con release.

However, due to demand by fans reading his livejournal and posting their desires on the Malhavoc message boards, Monte Cook released one more RPG product in early 2008, the Book of Experimental Might. This was quickly followed by the Book of Experimental Might II: Bloody, Bold and Resolute.