He was a general in the Confederate States Army during the American Civil War and served as Governor of Mississippi from 1865 to 1868, during Reconstruction.

He was educated in New Jersey and enrolled at United States Military Academy in the same class as Robert E. Lee and Joseph E. Johnston.

During the American Civil War, Humphreys raised a company and was commissioned a captain in the Confederate States Army in 1861.

At the Battle of Gettysburg in 1863, Humphreys's regiment was part of the force that attacked U.S. Army positions at the Peach Orchard, driving the U.S. soldiers back toward Cemetery Ridge.

He was subsequently promoted to brigadier general,[1] and remained in command until he was wounded in the battle of Berryville, Virginia, on September 3, 1864.

On October 26, provisional Governor William L. Sharkey received from President Johnson a pardon for Humphreys.