Upon graduation from VMI, Marshall was commissioned in 1902 as an infantry officer in U.S. Army. He served with distinction in the Philippine-American War and later in World War I. As part of the American Expeditionary Force to Europe during the Great War, he was assigned to the headquarters staff that planned American operations including the Meuse-Argonne Offensive. After the war, Marshall was an aid-de-camp to General John J. Pershing, U.S. Army Chief of Staff and the most senior officer in the U.S. Army.
In 1939, President Franklin Roosevelt named Marshall as U.S. Army Chief of Staff, making him responsible for increasing the size of military forces at the onset of World War II. During this time Marshall not only built and directed the largest American army in history, but he also became responsible for war strategy, including Operation Overlord, later known as the successful invasion of Normandy on "D-Day" in 1944. His peerless leadership during this time led to his promotion to five-star General of the Army.
Marshall retired at the close of World War II in 1945, having served 45 years in the military. But his retirement was short-lived. Only a few days after he stepped down from his post, Marshall re-entered public life at the request of President Harry Truman, to serve as a diplomat. By 1947, he had assumed the role of Secretary of State, and was tasked with another great challenge in his public service career—winning the peace and bringing sustainable liberty to a devastated, war-torn Europe.