Civil War Army Union Surgeon, Medal of Honor Recipient. Born to Dr. Alvah and Vesta Whitcomb Walker, she was one of five daughters and was next to the youngest followed only by her younger brother. She wore a female modified version of her male counterparts uniform and other clothing all throughout her life choosing this over female attire after her father, also a doctor, had told his daughters in their early years that he did not expect them to wear corsets (the undergarment of proper women of that time) as they were conducive to deformation of the female body. He merely instructed them to always dress respectfully. There is no evidence to suggest that she had any homosexual leanings, as she chose her clothing for practical reasons and not because she wanted to hide her sex. Mary merely chose to go about life in her own unique way, regardless what others may have thought of her appearance. She was a brave woman many years ahead of her time. She graduated from Syracuse Medical College in 1855 and for the first 3 years of the Civil War she was an army nurse and sometime spy. In 1864 she was commissioned as the first woman assistant surgeon in the U.S. Army. A few months after her graduation, she married a classmate, Albert Miller. The word "obey" was omitted from the ceremony and the young bride insisted on being called Dr. Miller-Walker. The marriage, however, was not a happy one. By the time the Civil War started the couple had separated but it would be years before Mary was able to secure a formal divorce. She never married again. On November 11, 1865, President Johnson signed a bill which presented her with the Medal of Honor for Meritorious Service. Dr. Walker displayed the medal proudly on the lapel of her jacket. She even received a replacement in 1907 and would frequently wear both medals together. In 1917, the MOH Board struck Dr. Walker's name from the list of recipients stating the citation should go only to a member of the armed services who had distinguished himself in "actual combat with an enemy..." Dr. Walker refused to give up her medal and wore it until her death in 1919. On June 10, 1977, the official records regarding Dr. Walker's case were corrected and 58 years after her death, her medal was finally reinstated. She passed away at the age of 86, from natural causes in the home of Mr. and Mrs. Frank Dwyer in Oswego. A plain funeral service without singing was held at her home. Only an American flag draped over her casket suggested any special recognition. She was buried in her black frock suit, not a dress.

Army Fort A. P. Hill in Virginia was originally named for a Confederate lieutenant general. On August 23, 2023, Fort A.P. Hill was renamed Fort Walker in honor of Dr. Mary Walker.