He received a military education at the Osaka Heigakuryo. He supported the Imperial party against the Tokugawa shogunate and became an officer in the Imperial Army. He lost the use of his right hand during the Satsuma Rebellion of 1877, the last samurai-led anti-imperial rebellion. Nevertheless, despite his handicap, he rose to high rank in the army. He was the first Inspector General of Military Education in 1898 and made that post one of the three most powerful in the Imperial Army. In it he worked to systematize military training.
He was the Army Minister during the Russo-Japanese War (1904-1905), serving under several Prime Ministers until 1910. That year he was appointed the first Governor-General of Korea.
This was his reward for working for Korean annexation throughout the first decade of the 20th century. As Governor-General, he encouraged a hard policy, and moved to crush all Korean opposition to Japanese rule, systematically suppressing all suspected anti-Japanese activity.
In 1916, he became Prime Minister. His cabinet consisted solely of career bureaucrats because he distrusted career civilian politicians. The major foreign policy events of his tenure concerned Japanese expansion. These consisted of the Nishihara Loans, which shored up the warlord government of Duan Qirui (Tuan Ch’i-jui) in China, the Lansing-Ishii Agreement in which the United States recognized Japan’s special interests in China and Japanese participation, along with other Allied forces, in the Siberian Intervention during World War I. He was an unpopular Prime Minister, identified with the hambatsu (the Choshu-born clique that controlled the government and the army). He was forced to resign after the 1918 Rice Riots, a nation-wide protest against the rise in the price of rice as a result of inflation. He died in 1919.