Although Edmonds was not an American citizen and had no obligation to participate in the war, she argued that she could not allow so many people to suffer while she had a comparatively easy life. In her memoir, Edmonds stated, "It is true, I was not an American—I was not obliged to remain here during this terrible strife . . . . It was not my intention, or desire, to seek my own personal ease and comfort while so much sorrow and distress filled the land." On May 17, 1861, Edmonds joined the Flint Union Greys of the Second Michigan, which was the first three-year regiment assembled in Michigan, and it was the first western regiment to reach Washington, D.C..
Edmonds served with the Second Michigan in various capacities until she contracted malaria in the spring of 1863. She had endured many injuries, which she had attended to herself in fear that a medical examination would lead the army to discover her true identity, throughout her time as a soldier. However, malaria cases were too dangerous not to be admitted into a hospital, so she was determined to desert rather than have her sex found out. She later returned to female clothing and rejoined the war as a female nurse.
Edmonds's duties as a soldier ranged from that of a male nurse to the regiment's postmaster, and finally a mail carrier. In addition to duties as a nurse, which included burying the dead soldiers, she picked up a gun and participated in the Battle of Williamsburg and the Seven Days' Battles. Edmonds witnessed some of the most infamous battles of