Along with Arthur MacArthur Jr., Bates was one of the last American Civil War veterans still on active duty in the United States military at the time of his retirement.

[1] He was educated at Washington University in St. Louis prior to joining the Army at the outbreak of the Civil War.

He later became an aide to General George G. Meade, reaching the brevet rank of lieutenant colonel for gallant and meritorious service in operations, resulting in the capture of Richmond and surrender of General Robert E. Lee's army in April 1865.

He was military governor of Cienfuegos in 1899 and went that year to the Philippines, where he conducted negotiations with the Sultan of Sulu.

Bates commanded a provisional division in maneuvers at Fort Riley and commanded the Departments of the Missouri and the Lakes from 1901 to 1904 and later the Northern Division for a year before serving as Chief of Staff of the United States Army from January 15 to April 13, 1906.