Born on January 8, 1860, as Sugataro Yabuki, the future Sen Katayama was the second son of an adopted (yoshi) father who four years later left the locally prominent Yabukis to become a monk. When he was 18, to circumvent military conscription, Sugataro was nominally adopted into the peasant household of Ikutaro Katayama, thereby obtaining his permanent name of Sen Katayama.
Katayama acquired a classical Confucian education in Okayama and then Tokyo, where he arrived at 21 at the height of the "people's rights" movement. Katayama studied at Hopkins Academy, Maryville College, Grinnell College, Andover Theological Seminary, and Yale Divinity School.
Back in Tokyo, Katayama soon began work at the Congregationalist Kingsley Hall, the first settlement house in Japan. This helped him come in contact with the incipient labor union movement, for which he founded Rodo Sekai (Labor World), the first labor paper in Japan. After helping organize the Society for the Study of Socialism in 1898, he joined those transforming it into the Socialist Society in 1900 and then became a founder of the abortive Social Democratic party of 1901, along with fellow Christians Isoo Abe, Kiyoshi Kawakami, Naoe Kinoshita, Kojiro Nishikawa, and atheist Denjiro (Shusui) Kotoku; though it had a mild, pacifistic platform, it was immediately dissolved by the authorities. Katayama's second journey to the United States and Europe (1903 - 1907) spanned the Russo-Japanese War, which he dramatically opposed by shaking hands with the Russian Georgi Plekhanov at the Sixth Congress of the Second International at Amsterdam in 1904. In Japan again, he encountered increasing governmental suppression of the Socialist movement, culminating in the precipitate execution of Kotoku in the "high treason trial" of 1910-1911. Katayama, nevertheless, fearlessly aided the Tokyo streetcar strike of 1911-1912 that won an outstanding victory for "organized" labor. But the costs were high. Katayama was imprisoned because of it; he felt forced to leave Japan in 1914. In Exile In America again, enduring hand-to-mouth poverty and suffering the divorce by his wife he had left in Japan with two children, having brought the older daughter to America, he played the role of interpreter of Japanese developments to the politically curious but ill-informed American Socialists. He ridiculed his more moderate rival labor leader, Bunji Suzuki, when he too visited the United States. In 1916 Katayama was invited to New York by the Dutch Socialist Rutgers, where he met Aleksandra Kollontai, Nikolai Bukharin, and Leon Trotsky and later helped found the American Communist party. In January 1920 he escaped the Palmer raids; in March 1921 he left for Mexico City for eight months on an assignment for the Comintern, after which he was invited to Moscow to accept a high position in the Comintern. The last 11 years of Katayama's life were spent serving the Comintern as one of the few Asians with a well-known revolutionary past. His knowledge of the Japanese Communist movement became increasingly vicarious. He traveled abroad again only briefly, to China in 1924. Toward the end of his life he became discouraged at the lack of success of the Communist movement in his own homeland. After his death on November 5, 1933, his bier was borne by Stalin and other dignitaries, and he was honored by burial within the Kremlin walls.
His Confucian idealism got a populist twist; he never lost an unshakable faith in individual and social perfectibility. With a warm, outgoing personality, Katayama made devoted friends, though a streak of irascibility also made him some enemies. One lifelong friend from this period was Seishichi Iwasaki of the Mitsubishi zaibatsu (a family-controlled commercial combine), who tolerated his friend's increasingly radical views and rescued him from debt, served as matchmaker in 1897, and later cared for his children. Iwasaki also helped him make his first trip to America (1884 - 1896).
Katayama had two children by his first wife, Fude, who died in 1903, and another daughter by his second wife, Hari Tama, whom he married in 1907.
