In 1987, he worked at Softdisk Inc., where he was both a programmer and the editor of Softdisk, a software bundle delivered monthly. Along with some of his co-workers, John Carmack, John Romero and Adrian Carmack, he founded id Software. He served as creative director and designer there, working upon games such as the Commander Keen series, Wolfenstein 3D, Spear of Destiny, and Doom.
After some disputes with John Carmack about the design for Doom, he left id Software in August 1993 to join Apogee/3D Realms. He was the game designer for Rise of the Triad, produced Terminal Velocity, and helped in varying degrees on Duke Nukem II and Duke Nukem 3D as well. He also worked on the Prey engine until August 12, 1996, when he left Apogee.
Hall co-founded Ion Storm with John Romero, where he produced Anachronox. The company also produced the 2000 Game of the Year, Deus Ex, in which Hall voiced one of the characters. He and John then founded Monkeystone Games, a company with the goal of producing mobile games in the then new mobile industry. He designed, and Romero programmed, Hyperspace Delivery Boy!, which was released on December 23, 2001.
He and Romero joined Midway Games in 2003, and Monkeystone closed in January 2005. Hall also left Midway early that year and did independent game consultation work out of Austin, Texas until in February he joined a startup company called KingsIsle Entertainment based in the same area.
Hall left Kingsisle and joined Loot Drop on January 1, 2011. Along with Loot Drop he unsuccessfully tried to crowdfund a game called Shaker on the crowdfunding platform Kickstarter during October 2012. Hall later tried to crowdfund another game on Kickstarter, Worlds of Wander, which was also unsuccessful in reaching its goal.
In March 2013, Hall joined PlayFirst as Principal Designer.
Hall is also the creator of the Dopefish, a large, green, buck-toothed, belching, dimwitted fish whose thought process is restricted to "Swim, swim, hungry". The Dopefish first appeared in Commander Keen episode IV, and references to it have appeared in many other video games since.
Hall provided the following voices for the computer role-playing game Deus Ex: Morpheus, a sentient AI; Howard Strong, a ruthless and cruel MJ12 operative; and Walton Simons, the nano-augmented Director of the Federal Emergency Management Agency (FEMA). He also voiced the project director in Deus Ex: Invisible War's opening cutscene, and PAL-18, Councilman Willis, Dr. Hush-Hush and Eddie the Chew in Anachronox. He was also the voice and likeness of the main antagonist of Rise of the Triad, El Oscuro, and also voiced the Death Monk enemies from the game.
Hall suffered a stroke on Tuesday, April 13, 2010. He was in rehabilitation until April 21, when he was released.