 Miller was a native of York County, South Carolina and worked as an attorney in Yorkville, the county seat, for several years before the war.Miller volunteered for military service for the Confederate States of America at the beginning of the Civil War, and organized a volunteer infantry company.Initially serving as a captain in the Army of Northern Virginia, he commanded a unit of skirmishers on September 17, 1862, during the Battle of Antietam (called the Battle of Sharpsburg in the south), assigned to locate Union Army positions.