Born in New York, she wasn't the first woman to graduate from medical school, but she was the only woman to graduate in her class of 1855. She married another medical student and kept her maiden name, which was very much against tradition during the era. She and her husband set up a practice together. Like many feminists of her time, she began wearing bloomers and tossed out her corset.
After four years of marriage, Dr. Walker and her husband separated. Divorce was almost unheard of, so years passed before it became finalized. In the meantime, she moved to Iowa. When the war broke out, she volunteered for the Union Army. In the 1860s, no female doctors existed in the army, and she was allowed to practice as a nurse.
The war dragged on, and Dr. Walker went to the battlefields of Tennessee, where General Thomas accepted her as a surgeon. Men of all ranks protested. In spite of the complaints, she was commissioned as a first lieutenant and assistant surgeon. She frequently crossed enemy lines to give aid to civilians. In April 1864, she was captured by the Confederates.
As a prisoner of war, Dr. Walker was sent to Richmond, Virginia. Later in the year, she was included in prisoner-of-war exchanges and released. Afterward, she worked in a female prison in Kentucky and a war-related orphanage in Tennessee. At the war's end, she was awarded the Medal of Honor for her service.
After the war, Dr. Walker went on the lecture circuit tirelessly working for women's suffrage and other women's rights. She had taken to wearing men's clothing and was arrested for it on several occasions. Ahead of her time, she was often considered too extreme by many of the well known suffragists.
In 1917, the U.S. Congress created a pension for Medal of Honor receivers, and in doing so, they withdrew the awards from many of the recipients. Dr. Walker's award was one of those withdrawn, but she continued to wear her medal for the rest of her life. She died two years later. Despite the controversy surrounding her choices, she remained proud of her achievements as a physician and women's rights advocate.
In 1977, Dr. Walker was posthumously rewarded with the reinstatement of her Medal of Honor.