During the war, he served as Chief of Ordnance in the Army of the Potomac, Department of the Ohio and the Army of the Cumberland. He was distinguished in the Battle of Fort Pulaski, Georgia, at the Battle of Chickamauga, the Battle of the Wilderness and the Second Battle of Ream's Station (New Market Heights). On June 26, 1902 or July 8, 1902, Porter received the Medal of Honor for the Battle of Chickamauga as detailed in the citation noted below. In the last year of the war, he served on the staff of Gen. Ulysses S. Grant, later writing a lively memoir of the experience, "Campaigning With Grant" (1897).