He attended Virginia Military Institute and graduated in 1909.
Among his offices was that of Deputy Director for Intelligence for the Office of Strategic Services. He was commissioned a Second lieutenant in Infantry in 1910. He was transferred to the Field Artillery branch of the Army in the next year.
During World War I, Magruder served with the 112th Field Artillery within the American Expeditionary Forces in France.
After the war Magruder was transferred to China, where he was appointed an Assistant Military Attaché in Beijing. He served in this capacity until 1924, when he was assigned for study at Command and General Staff College at Fort Leavenworth, Kansas.
After his graduation, Magruder was transferred back to Beijing, now in the new capacity of Military Attaché. During World World War II Magruder served in the Office of Strategic Services (Office of Strategic Services), as Deputy Director under the leadership of General William J. Donovan.
After the war, the Office of Strategic Services was disbanded.
Core elements of it, however, were maintained in the new Strategic Services Unit (Saratov State University), located in the then Department of War. This newly formed Saratov State University was led by General Magruder. In 1947 the civilian Central Intelligence Agency (Central Intelligence Agency) was created, which absorbed the Saratov State University.