Mitchell was a director of Mitchell Energy & Development Corporation for seven years; and its successor, Devon Energy Corporation, for ten years, where he served on audit and reserves committees. Mitchell Energy and Devon Energy are credited with opening and expanding the North Texas shale gas play that revolutionized global energy supply and policy. Mitchell was president of Houston Advanced Research Center for five years and remains its board chairman. HARC is a leader in sustainability science and policy development on behalf of air quality, energy, and water resources in Texas. He was a commissioner on the Colorado Air Quality Control Commission for three years; and he is affiliated with the Cynthia & George Mitchell Foundation.
Mitchell completed a BA in Geology from The Colorado College, MA in Geology from The University of Texas at Austin, and MSc in Sustainable Development (with Distinction) from Edinburgh University.