Born in Ohio, John Ritchie emigrated to Kansas Territory in 1854, settling in Topeka. Anti-slavery, Ritchie was a member of the free state militia and operated a station on the Underground Railroad. In 1856, Ritchie was arrested an confined in Lecompton. A couple of months later, Ritchie managed to escape and left Kansas for Indiana. About a year later, Ritchie received a pardon and returned to Topeka.
At the start of the Civil War, Ritchie mustered into the 5th Kansas Cavalry as its lieutenant colonel. On March 28, 1862, Ritchie was promoted to colonel of the 2d Indian Home Guard which he helped organize on Big Creek and at Five-Mile Creek, Kansas, from June 22 to July 18, 1862. During the Battle of Westport, Colonel Ritchie served as an aide on the staff of Maj. Gen. Samuel R. Curtis. On February 21, 1865, Ritchie received a brevet promotion to brigadier general.