Born in Oswego, in upstate New York, the daughter of Alvah and Vesta Walker. Her father was a country doctor as well as an ardent abolitionist. He was also an early proponent of women's rights and pursued equality and education for his five daughters.
Mary believed the fashions of the day, which included such binding clothing as corsets, were not healthy and advocated looser fitting clothing.
Walker taught school as a young woman to earn enough money to pay her way through Syracuse Medical College where she graduated as a doctor in 1855. She married a fellow medical school student, Albert Miller, and they set up a joint practice in Rome, New York (not Rome, Italy).
True to her progressive nature, when she married in 1856 she wore pants and a man's dress coat. She also kept her own last name. The practice did not flourish, as female doctors were generally not trusted or respected at that time. They divorced a few years later.
At the beginning of the Civil War, she volunteered for the Union Army as a civilian. At first, she was only allowed to practice as a nurse, as the Army had no female surgeons. During this period, she served at the First Battle of Bull Run (Manassas), July 21, 1861 and at the Patent Office Hospital in Washington, D.C.
She also worked as an unpaid field surgeon near the Union front lines, including the Battle of Fredericksburg and in Chattanooga after the Battle of Chickamauga. Finally, she was awarded a commission as a "Contract Acting Assistant Surgeon (civilian)" by the Army of the Cumberland in September, 1863, becoming the first ever female U.S. Army Surgeon.
She was later appointed assistant surgeon of the 52nd Ohio Infantry. During this service, she frequently crossed battle lines, treating civilians. On April 10, 1864, she was captured by Confederate troops and arrested as a spy (there appears to be some support to the idea that she may actually have been a spy). She was sent to Richmond and remained there until August 12, 1864 when she was released as part of a prisoner exchange.
She went on to serve during the Battle of Atlanta and later as supervisor of a female prison in Louisville, Kentucky and head of an orphanage in Tennessee. After the war, she was recommended for the Medal of Honor by Generals William T. Sherman and George Henry Thomas. On November 11, 1865, President Andrew Johnson signed a bill to present her the medal, specifically for her services at the First Battle of Bull Run (Manassas).
After the war, she became a writer and lecturer, supporting such issues as health care, temperance, women's rights and, quite naturally, dress reform for women. She wore men's clothes exclusively for the rest of her life.
In 1917, the U.S. Congress, after revising the standards for award of the medal so that it could only be given to those who had been involved in "actual combat with an enemy", revoked more than 900 previously awarded medals, including that of Dr. Mary Edwards Walker and, interestingly enough, William F. "Buffalo Bill" Cody. Although ordered to return the medal, she refused to do so and continued to wear it every day, albeit illegally, until her death.
Many of her supporters and relatives lobbied for years to have the Medal reinstated to her, and President Jimmy Carter did so on 10 June 1977. The order signed by President Carter cited Dr. Walker's "distinguished gallantry, self-sacrifice, patriotism, dedication and unflinching loyalty to her country, despite the apparent discrimination because of her sex".
Dr. Mary Edwards Walker was most definitely a transvestite but more than likely not a lesbian, even though according some biographer she seems to have been the lover of Belva Ann Lockwood.