Carmack grew up in Shawnee Mission, Kansas, part of the Kansas City Metropolitan Area, and became interested in computers at an early age. He graduated from Shawnee Mission East High School, then attended the University of Missouri - Kansas City for two semesters before dropping out to work as a freelance programmer. Softdisk in Shreveport, Louisiana hired Carmack, uniting him with John Romero and other future key members of id Software. In 1990, while still at Softdisk, Carmack, Romero, and others created the first of the Commander Keen games, a series which was published by Apogee Software, under the shareware distribution model, from 1991 onwards. Afterwards, Carmack left Softdisk to co-found id Software.
Carmack's most notable programming ventures are in the area of first-person shooter games. His programming skills contributed heavily to the development of seminal games of that genre: Wolfenstein 3D, Doom, Quake, as well as their newer versions (including Doom 3 and the rest of the Quake series). He has invented several computer graphic algorithms, notably surface caching and Carmack's Reverse. Carmack's game engines have been licensed for use in other influential first person action shooter games such as Hexen, Half-Life and Medal of Honor.
Carmack works to promote elements of open source thinking and fan feedback in his game designs. When the source code to Quake was stolen and circulated among the Quake community underground, a programmer unaffiliated with id Software used it to port Quake to Linux, and subsequently sent the patches to Carmack. Instead of pursuing legal action, at Carmack's behest id Software used the patches as the foundation for a company-sanctioned Linux port.
Carmack is also noted for his generous contributions to charities and gaming communities. Some of the recipients of Carmack's charitable contributions include his former high school, promoters of open source software, opponents of software patents, aerospace research, and game enthusiasts. In 1997 he gave away one of his Ferraris as a prize to the winner of the Quake "Red Annihilation" tournament, Dennis Fong.
On March 22, 2001, Carmack was inducted into the Academy of Interactive Arts & Sciences' Hall of Fame, an honor bestowed upon those who have made revolutionary and innovative achievements in the video and computer game industry.
In 2003, Carmack was one of the subjects of the book Masters of Doom, a chronicle of id Software and its founders.
Though Carmack is best known for his innovations in 3D graphics, he is also a rocketry enthusiast and the founder of Armadillo Aerospace.
Carmack met Katherine Anna Kang after she visited him at the id offices with a friend during QuakeCon '96. They married around January 2000 and their son Christopher Ryan was born at 12:50pm on August 13, 2004.
- John Carmack also makes a small appearance in Mike "Cyb" Watson's game Massmouth 2 as either an ally or an enemy depending on a path the player can choose in the level prior to his appearance.
- John is not related to Adrian Carmack.
- The Doom movie references the programmer by naming the movie's lead scientist "Dr. Carmack".
- When John was a child he once used a thermite based explosive to break into his school and steal a computer, there's an alternate timeline where he ends up killing the entire human race.
- Kushner, David (2003). Masters of Doom: how two guys created an empire and transformed pop culture, New York: Random House. ISBN 0375505245.