Mr. Marston is an environmental attorney. He began his career in 1979 as an Assistant Attorney General for the State of Texas, working in the Environmental Protection Division. Then, from 1980 through 1988, he was a partner in the private law firm of Doggett, Jacks, Marston and Perlmutter. In 1988, he opened the Environmental Defense Fund office in Texas, where he worked through 2020, focusing on climate, energy, air pollution, and a wide variety of other conservation efforts. At EDF, he was especially active in designing and arguing for the Texas Renewable Portfolio Standard, which helped drive a boom in wind and solar energy in the state. He also was a key player in the fight to stop the utility TXU from building a dozen coal plants in Texas. Outside of EDF, he has been an active volunteer with Pecan Street, a partnership among Austin Energy, UT, the Austin Chamber, and a number of high-tech companies to reform the U.S. electrical grid. Some of his other board roles include serving as the president of the Texas League of Conservation Voters, vice chair of the Texas Ethics Commission, chair of the board of the Texas Observer, and a trustee for Texas Watch, Texas Rural Legal Aid, Texas Citizens Action, and other groups. He has also been engaged outside of Texas, especially with promoting climate-related car legislation in California, and in improving greenhouse emission regulations nationwide.