William McIntosh Arnold enlisted on April 22, 1861 in Hancock County, Georgia, where he resided. He was mustered into service May 27, 1861 in Atlanta. Arnold was captain of his company, the Sidney Brown Infantry, Co. A of the 6th Regt. GA Vols. According to his service record, he fought at the Battle of Chancellorsville, Virginia (May 2-4, 1863) and was severely wounded in his arm and right lung. He was promoted to Major on June 16, 1863 and to Lieutenant Colonel on January 20, 1864. He died July 7, 1864.

His service record includes a letter he wrote in December of 1863, requesting a leave of absence of 20 days to visit his family in Sparta, Hancock County, Georgia.