Lawrence Mark Sanger was born in Bellevue, Washington, on July 16, 1968. His father, Gerry, was a marine biologist who studied seabirds and worked for the United States Fish and Wildlife Service. His mother, Lana, was a homemaker. When he was seven years old, Sanger's family moved to Anchorage, Alaska, where he was raised. As a teenager, he played the violin and created a text-based adventure game using the programming language BASIC. Sanger later recalled, "I decided I wanted to study philosophy and make it my life's work when I was about 16". When he was 17 years old, Sanger, inspired by the works of René Descartes, began to believe "only the things that he could directly perceive or that could be logically derived from what he perceived".
In high school, Sanger played piano, did cross country running and cross-country skiing, was a champion debater, and completed his graduation requirements a year early. According to The Atlantic, Sanger "excelled in high school" and "fits the profile of almost every Internet early adopter: he’d been a good student, played Dungeons & Dragons, and tinkered with PCs as a youth". After graduating from high school he enrolled at Reed College, beginning in the fall of 1986, majoring in philosophy.
In college, Sanger became interested in the Internet and its potential as a publishing outlet. He set up a listserver as a medium for students and tutors to meet for tutoring and "to act as a forum for discussion of tutorials, tutorial methods, and the possibility and merits of a voluntary, free network of individual tutors and students finding each other via the Internet for education outside the traditional university setting". He started and moderated a libertarian philosophy discussion list, the Association for Systematic Philosophy. In 1994, Sanger wrote a manifesto for the discussion group:The history of philosophy is full of disagreement and confusion. One reaction by philosophers to this state of things is to doubt whether the truth about philosophy can ever be known, or whether there is any such thing as the truth about philosophy. But there is another reaction: one may set out to think more carefully and methodically than one's intellectual forebears.
Sanger graduated from Reed College with a Bachelor of Arts in philosophy in 1991. He then pursued graduate studies at Ohio State University, where he earned his Master of Arts in philosophy in 1995 and his Ph.D. in philosophy in 2000. He is a professional epistemologist. His doctoral dissertation, completed under the philosopher George Pappas, was titled, Epistemic Circularity: An Essay on the Problem of Meta-Justification.
Around 1994, Sanger met Jimmy Wales after subscribing to Wales' mailing list, "Moderated Discussion of Objectivist Philosophy" (MDOP). Beginning in 1998, Sanger and a friend ran a website called "Sanger and Shannon's Review of Y2K News Reports", a resource for people, such as managers of computer systems, concerned about the year 2000 problem.
Nupedia was a web-based encyclopedia whose articles were written by volunteer contributors possessing relevant subject matter expertise and reviewed by editors prior to publication, and were licensed as free content. It was conceived by Jimmy Wales and underwritten by his company Bomis. Wales had interacted with Sanger on mailing lists. In January 2000, Sanger had e-mailed Wales and others about a potential "cultural news blog" project that would cover social and political issues that he had in mind after January 1, 2000, had passed and rendered his Y2K site obsolete. Wales replied with "Instead of doing that, why don't you come and work on this idea that I've had?", presented the idea of Nupedia to Sanger, and invited him to join the project. Sanger was hired as Nupedia's editor-in-chief. He began to oversee Nupedia in February 2000, developing a review process for articles and recruiting editors. Through working on Nupedia, Sanger "found that it was a fascinating problem to organize people online to create encyclopedias". Articles were reviewed through Nupedia's email system before being posted on the site.