Gilman's academic training is in astrophysics. He graduated from the University of California, Berkeley in 1967 with a bachelor's in astronomy. He received a Ph.D. in astrophysics from Princeton University in 1969. Gilman has taught and conducted research at the University of Minnesota, the Harvard Smithsonian Astrophysical Observatory and was a research associate at NASA's Institute for Space Studies.
Another phase of Gilman's life began in the mid 1970s when he decided that "the stars could wait, but the planet couldn't." He turned his attention to the study of global sustainability, futures research and strategies for positive cultural change. He and Diane designed and built their own solar home in 1975. In 1979 they founded the Context Institute, one of the earliest NGOs to focus on sustainability.
In 1983 the Context Institute began publishing In Context, A Quarterly of Humane Sustainable Culture, with Gilman as Editor. In Context won Utne Reader's Alternative Press Award for "Best Coverage of Emerging Issues" in 1991 and 1994.
Also in 1991, Gilman, who was publisher of the magazine In Context, wrote an article entitled “The Eco-village Challenge” that set out a definition of an ecovillage as a:
Gilman was a member of the Langley, Washington City Council until 2011. He has now focused his time on the Bright Future program, including the Bright Future Now course and the Bright Future Network.
