Florence Sabin was born on November 9, 1871, in Central City, Colorado. She was educated in Denver, Colorado, and Vermont and graduated from Smith College, Northampton, Massachusetts, in 1893. After teaching in Denver and at Smith to earn tuition money, she entered the Johns Hopkins University Medical School, Baltimore, Maryland, in 1896. While a student she demonstrated a particular gift for laboratory work; her model of the brain stem of a newborn infant was widely reproduced for use as a teaching model in medical schools. After graduation in 1900 she interned in Johns Hopkins Hospital for a year and then returned to the medical school to conduct research under a fellowship awarded by the Baltimore Association for the Advancement of University Education of Women. In 1901 she published An Atlas of the Medulla and Midbrain, which became a popular medical text. In 1902, when Johns Hopkins finally abandoned its policy of not appointing women to its medical faculty, Sabin was named an assistant in anatomy, and she became the first female full professor at Johns Hopkins in 1917.
For a number of years Sabin's research centered on the lymphatic system, and her demonstration that lymphatic vessels develop from a special layer of cells in certain fetal veins, rather than, as prevailing theory held, from intercellular spaces, established her as a researcher of the first rank. She then turned to the study of blood, blood vessels, and blood cells and made numerous discoveries regarding their origin and development. In 1924 she was elected president of the American Association of Anatomists, and in 1925 she was elected to the National Academy of Sciences; in both cases she was the first woman to be so honored.
In 1925 she accepted an invitation to join the Rockefeller Institute for Medical Research (now Rockefeller University), where she was also the first woman member. There she conducted research on tuberculosis, particularly the role of monocytes in forming tubercles. In 1934 she published a biography of her early mentor at Johns Hopkins, Franklin Paine Mall: The Story of a Mind.
Sabin retired from the Rockefeller Institute in 1938 and moved to Denver, where in 1944 she was named by the governor to a planning committee on postwar public health problems. She drew up a plan and lobbied successfully for a complete reorganization of the state health department. In 1948 she was appointed head of the Denver health department and served in that post until resigning in 1953. She died in Denver a short time later, on October 3, 1953. The state of Colorado subsequently chose her as one of its two representatives in Statuary Hall of the U.S. Capitol.