When Thorson was around fourteen, her mother helped her acquire a copy of GameMaker, a software tool to help develop video games. Through working in GameMaker, she was connected to others in online forums who were also interested in making games, including Chevy Ray Johnston. She developed a number of small pay-what-you-want games through GameMaker in high school and through college, including Jumper and several sequels, FLaiL, and An Untitled Story. Several of her games were described as "masocore", masochistic games that were extremely difficult for the player to complete; Thorson felt her goal was not to make her games near-impossible but instead to make games that helped direct the player to improve themselves so that the player could beat the challenges she made for them. Early games were published under the name Helix Games, but in April 2008, she rebranded it as Matt Makes Games (later, Maddy Makes Games), considering the name a more important brand for her work.
Thorson's goal in college was to get a computer programming degree and join up with a large game development studio, but as she progressed, she realized she could still make video games without having to be attached to a studio. Following her graduation, Thorson moved into a Vancouver apartment with Johnston where they shared game ideas. Most of these were browser games, and they successfully had a few of theirs published by Adult Swim Games on its site.
Thorson and Johnston were visited by friends they had made online. During a visit by Alec Holowka, he and Thorson participated in a local game jam and came up with an idea of a single-player platform game based on an out-of-shape archer trying to ascend a tower, collecting treasure and money to help with each attempt to climb it. They had considered pitching the idea to Adult Swim Games, but decided to expand the idea on their own, bringing in Johnston to help. The game morphed into a multiplayer battle game, where each player would try to defeat the others by shooting them with a bow-and-arrow while avoiding falling off the tower. Because of the frequent visitors to their apartment, they were able to gain feedback and improve the game to be a party-style title. This would ultimately become TowerFall, Thorson's first major commercial game.
Recognizing the potential success of the title, Johnston suggested that they get a house in Vancouver to bring in others to help, which they acquired around October 2012, calling it the "Indie House" and inviting other collaborators to join them. Thorson incorporated as Matt Makes Games Inc. shortly afterwards in November 2012. Later, Holowka recognized Thorson as TowerFall's main creator and relinquished his stake as a co-creator. Holowka remained on the game's development team as its composer. TowerFall was ultimately developed as an exclusive for the Ouya console. Following its initial release in 2013, the team reissued the game in 2014 as TowerFall: Ascension for most other gaming platforms with additional features. TowerFall: Ascension was critically praised, and within a month had brought in over US$500,000.