While in graduate school, Wales taught at two universities; however, he departed before completing a PhD to take a job in finance, and later worked as the Research Director of a Chicago, Illinois, futures and options firm. In 1996, he and two partners founded Bomis, an adult web portal featuring entertainment and adult content. The company would provide the initial funding for the peer-reviewed free encyclopedia, Nupedia (2000–03), and its successor, Wikipedia.
On January 15, 2001, with Larry Sanger and others, Wales launched Wikipedia—a free, open content encyclopedia that enjoyed rapid growth and popularity; as Wikipedia's public profile grew, he became the project's promoter and spokesman. He is historically cited as a co-founder of Wikipedia, though he has disputed the "co-" designation, declaring himself the sole founder.
Wales serves on the Wikimedia Foundation Board of Trustees, the non-profit charitable organization that he helped establish to operate Wikipedia, holding its board-appointed "community founder" seat. In 2004, he co-founded Wikia, a for-profit wiki hosting service. His role in creating Wikipedia, which has become the world's largest encyclopedia, prompted Time Magazine to name him in their 2006 list of "The 100 Most Influential People in the World".