Upon the outbreak of hostilities in the Pacific theater of World War II, Sugiyama served as the army’s de facto commander-in-chief until his removal by Prime Minister Hideki Tojo in February 1944.

Born to a former samurai family from Kokura (now part of Kitakyushu City), Fukuoka Prefecture, Sugiyama graduated from the 12th class of the Imperial Japanese Army Academy in 1901.

However, the failed coup d'etat of the February 26 incident in 1936 led to a purge of the Kōdōha from positions of authority and Sugiyama was promoted to full general in November 1936.

When hostilities broke out near the Marco Polo Bridge, Sugiyama pushed Konoe for retaliation against China, thereby giving rise to the Second Sino-Japanese War.

[6][4] By September 3, 1940, Hajime Sugiyama succeeded the elderly Prince Kan'in Kotohito as Chief of the Imperial Japanese Army General Staff.

[8] On September 5, 1941, Emperor Hirohito challenged his confidence in a quick victory over the Western powers by berating him for erroneously predicting in 1937 that Japan's invasion of China would be completed within three months.

[11][12] In a matter of months, the Empire of Japan conquered a broad swathe of territory in Southeast Asia and the western Pacific including Malaya, the Dutch East Indies, Burma, and the Philippines.

[4][2] In July 1945, he was asked to take command of the First General Army, which directed defenses of eastern half Japanese mainland against the anticipated Allied invasion.

[7][18][page needed] Ten days after the surrender of Japan, after finishing preparations for the final dissolution of the Imperial Japanese Army as dictated by the victorious Allied Powers, Sugiyama committed suicide by shooting himself four times in the chest with his revolver while seated at his desk in his office.