In 1912, Brereton transferred to the Aviation Section of the Signal Corps and became a pilot the following year. When the United States entered World War I in April 1917, he was among the first aviators of the American Expeditionary Forces (AEF) in France. As commander of the 12th Aero Squadron between March and October 1918, he shot down four German planes and earned the Distinguished Service Cross.
Following occupation duty in Germany, Brereton served as air attaché in Paris from 1919 to 1922. He next was an instructor at Kelly Field, Texas, and Langley Field, Virginia, and commanded the 2nd Bombardment Group. He graduated from the Command and General Staff School in 1927 and then held a succession of assignments. Promoted to temporary brigadier general in 1940, he commanded the 17th Bombardment Wing at Savannah, Georgia. The next year, he advanced to major general and commanded the Third Air Force at Tampa, Florida.
In November 1941, Brereton took command of the Far Eastern Air Force in the Philippines. General Douglas MacArthur refused him permission to launch an immediate strike on Formosa following the Japanese attack on Pearl Harbor, and as a result, nearly half of his planes were destroyed in the Japanese attack of 8 December 1941. Following the fall of the Philippines, Brereton took command of Tenth Air Force in India.
In June 1942, he went to Cairo to command the Middle East Air Force, later designated the Ninth Air Force. He planned the air strikes against the oil refineries of Ploesti, Romania, in August 1943. One year later, as a lieutenant general, Brereton took command of the First Allied Airborne Army, which participated in Operation market-garden, the unsuccessful Allied invasion of the Netherlands. In December 1944, during the Battle of the Bulge, Brereton's planes dropped supplies to the encircled 101st Airborne Division at Bastogne, Belgium, and in March 1945, they dropped troops near Wesel, Germany, in Operation varsity to secure a bridgehead over the Rhine.
After the war, Brereton again commanded the Third Air Force at Tampa, Florida. He transferred to the U.S. Air Force in 1947 and was a member of the Military Liaison Committee of the Atomic Energy Commission before retiring in 1948. Brereton published his memoirs in 1946. He died in Washington, D.C., on 19 July 1967.
Brereton, Lewis Hyde. The Brereton Diaries: The War in the Pacific, Middle East and Europe, 3 October 1941–8 May 1945. New York: William Morrow, 1946.; Craven, Wesley Frank, and James Lea Cate, eds. The Army Air Forces in World War II. Vol. 4, The Pacific: Guadalcanal to Saipan, August 1942 to July 1944. Washington, DC: Office of Air Force History, 1983.; Winton, John. War in the Pacific: Pearl Harbor to Tokyo Bay. New York: Mayflower Books, 1978.