Stephan Washington was born around 1833 in Charlottesville, Virginia, and worked as a farmer before the war. He enlisted in the Union army on November 9, 1862, in Bayou Lafourche, Louisiana, and mustered in as a private in Company A of the 3rd Louisiana Native Guards Infantry Regiment in New Orleans on November 24. His enlistment records describe him as 5 feet, 9 inches tall, with black eyes, black hair, and a black complexion. He may have been a runaway slave, as the regiment was composed primarily of former slaves who had fled to Union lines. 

That December, the army assigned the regiment to harvest sugar in the fields in Bayou Lafourche. After finishing this task, they joined the Union forces under General Nathaniel P. Banks and took part in the Siege of Port Hudson. On June 6, the army restructured the regiment and renamed it the 3rd Corps d'Afrique Infantry Regiment. The men remained at Port Hudson until March 23, 1864, when the army sent them to Alexandria, Louisiana. They took part in the failed Red River Campaign, during which the Union military attempted to establish a base in western Louisiana for use in future expeditions in Texas. During the campaign, the army restructured the regiment once again, turning it into the 75th USCT Infantry Regiment on April 4. The men were stationed in Morganza, Louisiana, until February 1865. Washington served as the company cook that fall, and he mustered out on November 25, 1865, after completing his three-year term of service. He disappeared from the historical record after leaving the army.