He married Gerry Stowell after World War II and they had three children – Richard, Robert and Rustin Weaver. Dennis Weaver was a vegetarian since 1958 and student of yoga and meditation since the 1960s and a devoted follower of Paramahansa Yogananda, the Indian guru who established the Self Realization Fellowship in the US.
The "Earth Ship", the personal home he commissioned architect Michael Reynolds to design and build in Ridgway, Colorado during the late 1980s, incorporated recycled materials in its construction and featured advanced eco-technologies.
In July 2003, Weaver lost a daughter-in-law, Lynne Ann Weaver (who was married to his son, Robby Weaver), in Santa Monica, California, when a car driven at high speed plowed through shoppers at an outdoor bazaar. She was one of ten people killed in the incident.
He was renowned as an environmentalist, promoting eating lower on the food chain, use of alternative fuels such as hydrogen, and wind power, through an educational organization he founded, The Institute of Ecolonomics. Ecolonomics is a neologism formed by combining "ecology" and "economics".
He was also involved with John Denver's WindStar Foundation and he founded an organization called L.I.F.E. (Love is Feeding Everyone) which provided food for 150,000 needy people a week in Los Angeles.
Weaver was also active in liberal political causes. He used his celebrity status in instrumental roles as a fundraiser and organizer for George McGovern's campaign for president in 1972.]
In 2004, he led a fleet of alternative fuel vehicles across America in order to raise awareness about America's dependence on oil.
Weaver was consistently involved with the annual Genesis Awards, which were created by The Ark Trust to honor those in the media who bring attention to the plight and suffering of animals.
There will come a time … when civilized people will look back in horror on our generation and the ones that preceded it: the idea that we should eat other living things running around on four legs, that we should raise them just for the purpose of killing them! The people of the future will say “meat-eaters!” in disgust and regard us in the same way we regard cannibals and cannibalism – Dennis Weaver