Caroline Purnell was born in Frederick, Maryland, and graduated from Woman's Medical College of Pennsylvania in 1887. She was Instructor in Gynecology at Woman's Medical College from 1888 to 1893 and later became the Clinical and Associate Professor in Gynecology. Dr. Purnell served as Chief of Gynecological Staff at Woman's Hospital from 1900 to 1923, a position she held until her death. She was also consulting specialist at West Philadelphia Hospital for Women, the Frankford Hospital for the Insane, the Morristown and Wernersville Hospitals, and the Moyamensing Prison.

During World War I, Dr. Purnell served as Special Commissioner of the American Women's Hospitals (AWH) in France. The AWH was founded to relieve the post-war suffering brought on by famine and disease in Europe and Russia, and advance the worldwide position of women in the medical profession.

As commissioner she secured food, fuel, clothing and medical supplies and established hospitals and dispensaries for soldiers and civilians in Luzancy, La Ferte Milon, and Soissons. The AWH records describe Dr. Purnell as having a knack for organization, management, a "broad catholic view of looking at things" and "a splendid executive ability."

Dr. Purnell also served as the liaison between the AWH and the Red Cross, the American Committee for Devastated France, and the Serbian Legation in Paris. While in France she became ill and was forced to return to the United States, where she dedicated her energies to fundraising for AWH. For this work she received two honorary medals from the French Government.