Studying chemistry at the University of California, Erlanger received his B.S. degree there, then went to Johns Hopkins University, where he obtained his M.D. degree in 1899. After a year of hospital training at the Johns Hopkins Hospital, he was appointed assistant in the Department of Physiology there, subsequently serving as instructor, associate, and associate professor. He was appointed the first professor of Pphysiology in the newly established Medical School of the University of Wisconsin, where one of his pupils was H. S. Gasser, who later collaborated with him on his Nobel Prize winning work. In 1910 he was appointed professor of physiology in the reorganized Medical School of Washington University.

Erlanger has also worked on the metabolism of dogs with shortened intestines, on traumatic shock, and on the mechanism of the production of sound in arteries. He received honorary doctorates of the Universities of California, Wisconsin, Pennsylvania, and Michigan. In 1946 he retired as chairman of Washington University Medical School.