Ernest August Janson was born on 17 August 1878 in Brooklyn, New York. He enlisted in the U.S. Army from that state, served for nearly a decade before enlisting in the U.S. Marine Corps at Bremerton, Washington in June 1910. Promoted to the rank of Corporal in March 1911, he re-enlisted in June 1914. The following month Janson reported for sea duty on board USS Nebraskaand, in August, was promoted Sergeant. In early 1915 he had temporary duty on board the armored cruiser Montana before returning to the Nebraska and, from October 1916 to May 1917, served ashore at Norfolk, Virginia.

The transport DeKalb took Sergeant Janson (serving under the name Charles F. Hoffman) to France in June 1917 as a member of the first contingent of U.S. ground forces to arrive in the war zone. With a wartime rank of Gunnery Sergeant, he served on the Western Front with the Forty-Ninth Company, Fifth Regiment, Second Division. On 6 June 1918, during fighting near Chateau-Thierry, France, he attacked and drove off an enemy machine-gun unit that threatened the position recently taken by his unit. For his "conspicuous gallantry and intrepidity" on this occasion, in which he received severe wounds, he was awarded the Medal of Honor by both the U.S. Navy and the U.S. Army.

Returning to the United States in November 1918, as World War I's active combat came to an end, Janson reverted to the rank of Sergeant and re-enlisted in the Spring of 1919. He subsequently spent seven years on recruiting duty in New York City. Beginning in July 1926 he briefly served at the Marine Barracks, Quantico, Virginia. Reinstated in the rank of Gunnery Sergeant, he was promoted to Sergeant Major in August 1926 and placed on the retired list a month later. Ernest A. Janson died on 14 May 1930 and is buried at Evergreen Cemetery, Brooklyn, New York.