Stewart is a cofounder of GBN and president of The Long Now Foundation, an organization that promotes long-term thinking by exploring “whatever may be helpful for thinking, understanding, and acting responsibly over long periods of time.” He is perhaps best known as the founder, editor, and publisher of the Whole Earth Catalog and the creator of The WELL, which now has 11,000 active users worldwide and is considered a bellwether of the genre. Since 1989, he has served on the board of the Santa Fe Institute, an organization dedicated to multi-disciplinary research in the sciences of complexity. He is also a founding member of the board of directors of the Electronic Frontier Foundation.

Stewart is the author of many pioneering books, including The Whole Earth Catalogues (1968-1985), The Clock of the Long Now (1999) and The Media Lab: Inventing the Future at MIT (1987). His book How Buildings Learn: What Happens After They’re Built has been dubbed "a classic and possibly a work of genius" and has been used as a text by computer systems designers as well as building preservers, architects, and many lay building users. In his new book Whole Earth Discipline: An Ecopragmatist Manifesto (2009), Stewart offers an eloquent, deeply researched argument for why his fellow environmentalists (and the rest of us) must embrace urbanization, nuclear power, and biotechnology in order to create a sustainable future.