He went to Tokyo and attended school while working as a printer. In 1884 he went to America where, in spite of financial difficulties, he managed to study at Yale University and elsewhere.
He returned to Japan in 1896 and the following year opened a settlement house called Kingsley Hall in the Kanda area of Tokyo. He thereafter participated in the newly organized trade union movement, publishing a magazine called Rodo Sekai.
After Kotoku’s execution on charges of plotting against the emperor, he acted as leader of the Tokyo streetcar strike in 1911-12. He went to America in 1914, where he was active among the socialist leaders of the Japanese community in America. In 1921 he went to the Soviet Union, where he was appointed a member of the permanent executive committee of the Comintern and became a leader in the international Communist movement. He took part in the drafting of the 1927 Thèse and the 1932 Thèse, and died in 1933 in Moscow. He was buried in the Kremlin.
In 1900 he joined Kotoku Shusui in forming the Shakai Sliugi Kyokai (Socialist League), and in 1901 they helped to form the Shakai Minshuto (Social Democratic Party), which was outlawed the same day it was founded. He thus was one of the pioneers of the Japanese socialist movement. He opposed the Russo-Japanese War and in 1904 attended the Second International in Amsterdam as representative from Japan, where he shook hands with the Russian delegate Plekhanov in a gesture of protest against the war. After returning to Japan, he opposed Kotoku’s calls for direct social action, advocating parliamentary reforms instead.