Clark was appointed to the US Military Academy at West Point and graduated in 1868. He was assigned as a Second Lieutenant with the U.S. 2d Cavalry Regiment, to which he belonged for the remainder of his short career. He joined the staff of General George Crook at the end of August, 1876, when Crook rejoined the columns of General Alfred Terry and Colonel John Gibbon after the Battles of the Rosebud and the Little Bighorn during the Great Sioux War of 1876. Clark was thus present for Crook's pursuit of the Lakota during the late summer and fall of 1876, including the so-called "Starvation March" and the Battle of Slim Buttes. He served in a number of staff assignments for General Philip Sheridan and died suddenly at the age of 39, in Washington, DC in 1884 while on special duty with Sheridan.