In 2008, Frank Li found that Git was a very good version control system, but it lacked a good GUI client. The idea for a Git client as a Windows shell integration was inspired by the similar client for SVN named TortoiseSVN.
Frank studied the source code of TortoiseSVN and used it as a base for TortoiseGit. He then started the project, registered the project at code.google.com and put the source code online.
At the end of 2010 Sven Strickroth joined the TortoiseGit project. Then, he became the current maintainer few years later.
From August 2015, GoogleCode was shut down and the TortoiseGit project established their website tortoisegit.org and migrated the main repository and issue tracker to GitLab.
As Git became more stable it attracted more and more users who also started using TortoiseGit as their Git client.