Gasser, the son of a country doctor from Platteville, Wisconsin, was educated at the University of Wisconsin and at Johns Hopkins University. Having qualified as a physician in 1915, he moved to Washington University, St. Louis, to take up an appointment as professor of pharmacology. Here he joined his old teacher, Joseph Erlanger, in a famous collaboration that resulted in their sharing the 1944 Nobel Prize for physiology or medicine for work on the differentiated function of nerve fibers. In 1931 Gasser was appointed to the chair of physiology at Cornell Medical School. Finally, in 1935, he was made director of the Rockefeller Institute in New York, a post he retained until his retirement in 1953.