Van Fleet commanded the 8th Infantry Regiment for three years and led it into combat in Europe in World War II, participating in the D-Day landings on Utah Beach in June 1944. Although widely regarded as an outstanding officer, he was blocked from promotion because the Army Chief of Staff, General George Marshall, erroneously confused Van Fleet with a well-known alcoholic officer with a similar name. When Marshall learned of his mistake, Van Fleet was soon promoted to divisional and corps command. He later served with General George S. Patton's U.S. Third Army.
In 1946, Van Fleet was sent to Greece, as the executor of the "Truman Doctrine" where he was instrumental in the outcome of Greek Civil War by providing advice to the Greek government and 250 military advisors, as well as administering $400 million in aid. A square in the Northern Greek city of Kastoria was named after him for many years. It recently was changed due to the anti-American sentiment in Greece.
Van Fleet was Commanding General of the U.S. Second Army from August 10, 1950 to April 11, 1951.
In 1951, he replaced General Matthew B. Ridgway as commander of the U.S. Eighth Army and United Nations forces in Korea. He continued Ridgway's efforts to strengthen the Eighth Army in its campaign against numerically superior Communist foes. He lost his only son, an Air Force officer, in the Korean War.
In 1957, General Van Fleet was the moving spirit behind the establishment in New York of the Korea Society, the first nonprofit organization in the U.S. dedicated to the promotion of friendly relations between the peoples of the United States and Korea "through mutual understanding and appreciation of their respective cultures, aims, ideals, arts, sciences and industries."
Van Fleet died in 1992 in Polk City, Florida several months after reaching his 100th birthday. He was the oldest living general officer in the United States. Van Fleet was buried in Section 7 of Arlington National Cemetery.
Shortly after his death, The Korea Society established its annual James A. Van Fleet Award to recognize those who have made outstanding contributions to closer U.S.-Korea ties. The Gen. James A. Van Fleet State Trail, running from Polk City, Florida to Mabel, Florida, is also named in his honor. The military sciences / ROTC building on the campus of the University of Florida is named Van Fleet Hall.
In July 2001 a biography entitled "WILL TO WIN: The Life of General James A. Van Fleet," by Paul F. Braim, was published by the Naval Institute Press.