George Henry Decker was born in Catskill, New York, on 16 February 1902. He graduated from Lafayette College in 1924 and was commissioned a second lieutenant. He was assigned to the 26th Infantry at Plattsburg Barracks from 1924 to 1928. In 1926, he married Helen E. Inman. From 1928 to 1931, he was stationed in Hawaii with the 35th Infantry. In 1930, he was promoted to first lieutenant and then graduated from Infantry School in 1932. From 1932 to 1935, he was assigned to Fort Benning with the 29th Infantry.
Decker was promoted to captain in 1935; he graduated from the Command and General Staff School in 1937. From 1937 to 1940, he served with the 10th Infantry at Forts Thomas and McClellan, and with the 9th Infantry at Fort Bragg. In 1941, Decker was made a major and temporary lieutenant colonel.
From 1941 to 1942, he served on the War Department General Staff in the Office of the Assistant Chief of Staff for Supply. In 1942, he received a promotion to temporary colonel. From 1942 to 1944, Decker was the deputy chief of staff of the Third Army at Fort Sam Houston. He then served as deputy chief of staff and chief of staff for the 6th Army in the Pacific. Decker participated in the campaigns from New Guinea to the Philippines. He was made a temporary brigadier general and temporary major general, in 1944 and 1945, respectively.
After World War II, Decker returned to the United States as an officer in the Army Ground Forces and Army Service Forces. He was deputy commander and chief of staff of United States Forces, Middle Pacific, Hawaii, from 1946 to 1948. He was made a permanent lieutenant colonel in 1947 and a full colonel in 1948. Decker led the 5th Infantry Division until 1950, and then served in the Office of the Comptroller of the Army from 1950 to 1952. In 1952, he was promoted to temporary lieutenant general and served as comptroller of the Army until 1955.
In 1953 and 1954, Decker received the permanent ranks of brigadier general and major general. In 1956, he became a temporary general and then served as deputy commander in chief of the United Nations Command and commander of United States Forces and Eighth Army, Korea, from 1957 to 1959. Decker was vice chief of staff of the Army from 1959 to 1960. When General Lemnitzer was promoted to Chairman of the Joint Chiefs of Staff, Decker took his place as Army Chief of Staff. Decker served in this post from 1 October 1960 to 30 September 1962. While he served as Chief of Staff, Decker expanded the Army to 16 divisions, oversaw crises in Berlin, and increased special warfare forces. He retired from active duty in 1962. Decker died in Washington, D.C., on 6 February 1980.