Dr. Wagner was born in Minden, New York, educated at Cornell University, and received the M.D. (1882) from the Columbia University College of Physicians and Surgeons. He served as Medical Superintendent of the Binghamton State Hospital, the Utica State Hospital, and the Presbyterian Hospital in New York City (1882–84), served as an expert witness in forensic trials, was a lecturer on insanity at the Sage School of Philosophy of Cornell University (1896–1901), and served as a Trustee of Cornell (1896–1906).
Dr. Wagner served as an associate editor of The American Journal of Insanity (1884–92). He was Secretary-Treasurer (1909–15), Vice President (1915–16), and President of the American Medico-Psychological Association (1916–17).