In the Mexican–American War, Miller held a captaincy within the 2nd Illinois Regiment of Volunteers and was wounded at the Battle of Buena Vista.
Mayor Miller was a passenger on the Pacific Railroad excursion train that crashed through the temporary bridge over the Gasconade River on November 1, 1855.
In February, 1862, Miller was given the command of the 18th Missouri Volunteer Infantry following the removal of W. James Morgan as colonel.
In the Battle of Shiloh, Miller commanded the 2nd Brigade in Benjamin Prentiss' division and took part in the fighting in the Hornet's Nest.
Following the war, he managed portions of the Pacific Railroad, dabbled in St. Louis, Missouri area real estate and held the position of vice-president within the Society of the Army of the Tennessee in 1893.