From 1991-1997, Stephenson was employed in the private sector at Los Alamos National Laboratory as an occupational health professional. From 1988-1991, Stephenson attended Colorado State University where he received his Ph.D. in Environmental Health.
Stephenson's interestes in Environmental Health arose from his tenure with the United States Peace Corps in Mali, West Africa where he worked with rural villages to improve water quality. He is active in research in the areas of exposure assessment and environmental aerosol monitoring and has garnered extramural funding and published peer-reviewed articles related to these topics.
He is married and has two sons. He is an avid squash player and likes to hunt and fish in the mountains and streams of Idaho.