Gerard McMahon studied Political Economics at the John Hopkins University, before specializing in Agricultural Economics at the University of Missouri.
He was in charge of the United States Geological Survey Water Quality Assessment Program (NAWQA), studying the effects of urbanization on stream ecosystem. He also worked for the USGS as a geographer on several other projects and led a multi-disciplinary team of scientists in a year-long effort to develop a 10-year USGS Geography Science Plan.
Since 2011, he is director of the Department of Interior Southeast Climate Science Center. This Climate Science Centers provide scientific information, tools and techniques that land, water, wildlife and cultural resource managers and other interested parties can apply to anticipate, monitor and adapt to climate and ecologically-driven responses at regional-to-local scales.