He is an active contributor within the free and open-source software community, most prominently in the San Francisco Bay Area, where he lives.

[4] Preston-Werner is also the creator of the avatar service Gravatar,[5] the TOML configuration file format,[6] the static site generator software Jekyll,[7][8] and the Semantic Versioning Specification (SemVer).

[11] As an active contributor to the open-source developer and hacker culture, most prominently in areas involving the programming language Ruby,[12] he has written articles regarding his philosophies and opinions on various issues.

[14] In an article published by Hacker Monthly in 2010, Preston wrote about his passion for ensuring that developers document the code they write so others can easily understand how it works.

[11] Preston-Werner co-founded GitHub in 2008 with Chris Wanstrath, P. J. Hyett and Scott Chacon, as a place to share and collaborate on code.

[12] Julie Ann Horvath, a GitHub programmer, alleged in March 2014 that Tom Preston-Werner and his wife Theresa had engaged in a pattern of harassment against her that led her to leave the company.

GitHub's new CEO Chris Wanstrath said the "investigation found Tom Preston-Werner in his capacity as GitHub's CEO acted inappropriately, including confrontational conduct, disregard of workplace complaints, insensitivity to the impact of his spouse's presence in the workplace, and failure to enforce an agreement that his spouse should not work in the office.