A native of Pendleton, South Carolina, William G. Washington enlisted in the Army in 1914 at Fort Oglethorpe, Georgia, and rose through the ranks from private to sergeant major. He completed two tours of duty in the Philippines, served as post ordnance sergeant of harbor defense at Columbia River in Oregon and at the Presidio in San Francisco, and was sergeant major of the Savannah Depot in Illinois.
In May 1942, he accepted a commission as an ordnance captain. He commanded a company at Fort Sill, Oklahoma, and then was transferred to Raritan Arsenal, New Jersey, where he served as adjutant, reception officer, and supply officer. In November 1942, he was assigned to the Ordnance Replacement Training Center (ORTC) at Aberdeen Proving Ground as an instructor in the military training division. He then took command of the ORTC's Company D, 2nd Ordnance Training Regiment. He was the first African American officer to command a company at Aberdeen.
Promoted to major in October 1943, he retired in July 1944 after an unblemished record of thirty years service. His commander, Colonel James W. Mosteller, commended him for "loyalty to your government and your willingness to serve in any capacity for the good of the service." Major Washington set an example of selfless service in a period when African American soldiers had to endure the inequities inherent in a segregated army.