A "lifelong environmentalist" refers to a person who has been committed to protecting and preserving the environment for their entire life. They care deeply about issues such as pollution, conservation, and sustainability. Full definition
Katy is a Massachusetts native and lifelong environmentalist. (bostonmamas.com)
My father is a lifelong environmentalist, educator and private school administrator who in retirement is an accomplished and successful community organizer and liberal / radical political activist. (alltogetherdiaper.com)