Reed spent his childhood in Murfreesboro, North Carolina with his mother and her family while his father, a traveling Methodist minister, went on speaking tours. Reed went on to attend the University of Virginia and received his M.D. degree. He did this two months before his 18th birthday, making him the youngest-ever recipient of that degree from that university.
Reed went on to earn a second M.D. from New York University’s Bellevue Hospital Medical College in 1870. He then worked for the New York Board of Health until 1875. Unhappy with his position, he decided to join the US Army Medical Corps. After passing a 30-hour examination, he was enlisted to the medical corps as an assistant surgeon.
Reed went on to join the staff of the George Washington University School of Medicine and the Army Medical School in Washington, DC, in 1893. There he served as professor of Bacteriology and Clinical Microscopy. In addition to teaching, he also worked on medical research projects and curated the Army Medical Museum.