He was educated at Saint James College in Hagerstown, Maryland.
He moved with his family to Chicago, Illinois in 1857. In 1862, Clarkson married Mary Beecher Matteson. They had five children.
On April 16, 1861, Clarkson enlisted at Chicago as a private in Smith"s Independent Illinois Light Artillery.
He was promoted to corporal on May 2, 1861 and to sergeant on July 16, 1861. He mustered out with the battery on the same date.
The battery was reorganized and he reenlisted the same day as a private in Battery A, 1st Illinois Light Artillery and mustered out November 27, 1861 at Pilot Knob, Missouri. Clarkson subsequently transferred to the 13th Illinois Cavalry on December 31, 1861, to accept a commission as a first lieutenant, where he was assigned to serve as adjutant for the regiment.
Clarkson was then appointed to the staff of Brigade
General John West. Davidson. He rose through the ranks and was promoted to major on December 14, 1863, the same day that he was mustered out of the regiment. The following day, he began service with the 3rd Arkansas Cavalry, a regiment he helped raise and commanded until the end of the war.
He mustered out of the service on September 10, 1864.
In March 1866 Clarkson settled in Nebraska with his family and became postmaster in Omaha. He became active with the G.A.R., serving as Commander of the Department of Nebraska in 1890, Junior Vice Commander-in-Chief of the G.A.R. in 1892, and finally as Commander-in-Chief of the G.A.R., 1896-1897.
He was elected May 23, 1898 as general manager of the Transport-Mississippi International Exposition. Clarkson died January 16, 1915 in Newberg, Oregon.
He is buried in Omaha at Prospect Hill Cemetery, where his headstone is missing.