Hall was on vacation in the United Kingdom in the summer of 1914, when World War I began. Posing as a Canadian, he enlisted in the British Army, serving in the Royal Fusiliers as a machine gunner during the Battle of Loos. He was discharged after his true nationality was discovered, and he returned to the United States and wrote his first book, Kitchener's Mob (1916), recounting his wartime experiences.
Returning to France, Hall joined the Lafayette Escadrille, a French-American flying corps, before the United States officially entered the war. Hall was awarded the Croix de Guerre with five palms and the Médaille Militaire. When the United States entered the war, Hall was made a Captain in the Army Air Service. There he met another American pilot, Charles Nordhoff. After being shot down, Hall spent the last months of the conflict as a German prisoner of war. He was awarded the French Légion d’Honneur and the American Distinguished Service Cross.
After the war, Hall spent much of his life on the island of Tahiti, where he and Nordhoff, who had also moved there, wrote a number of successful adventure books (including the Bounty trilogy), many of which were subsequently made into movies. In 1925 Hall married Sarah (Lala) Winchester, who was part-Polynesian. They had two children: the cinematographer Conrad Hall (1926–2003) and Nancy Hall-Rutgers (born 1930).
Hall died in Tahiti and is buried on the hillside property just above the modest wooden house he and Lala lived in for many years.