Gregory A. Petsko (born August 7, 1948) is an American biochemist and member of the National Academy of Sciences, the National Academy of Medicine, the American Academy of Arts and Sciences, and the American Philosophical Society. He is currently Professor of Neurology at the at Harvard Medical School and Brigham and Women's Hospital. He formerly had an endowed professorship (the Arthur J. Mahon Chair) in Neurology and Neuroscience at Weill Cornell Medical College and is still an adjunct professor of Biomedical Engineering at Cornell University, and is also the Gyula and Katica Tauber Professor, Emeritus, in biochemistry and chemistry at Brandeis University.