He went to America as a boy and spent five years from 1907 studying under difficult circumstances in Canada. During this period he became a Unitarian and developed an interest in socialism. After returning to Japan, lie attended the Third High School and Tokyo Imperial University.
Upon completing the zoology course of the latter, he became a lecturer in Doshisha and Kyoto universities and devoted himself to sexology. In 1922, when Margaret Sanger visited Japan, he became interested in the birth-control movement and worked to promote it. He conducted a survey of the sexual activities of Japanese students in various colleges, which was highly praised by specialists in the field. These activities brought him into contact with members of the working class, and in 1924 he became head of the Kyoto Workers’ School.
In 1925-26, when steps were taken to suppress left-wing students in the Kyoto schools, Yamamoto became implicated and was deprived of his university teaching positions. He later became active in the Japan Farmers’ Union.
In 1927 he was made chairman of the Kyoto Prefecture branch of the Rodo Nominto (Labor Farmer Party). In 1928, in the first election carried out under the universal manhood suffrage law', he was elected to the Diet as a member of the same party, thus becoming the sole Diet member representative of a communist type party. In the 56th session of the Diet in 1929, he vigorously attacked the Peace Preservation Law, which was being utilized by the police for the harrassment of left-wing activities. As a result, he was attacked the same year at an inn in the Kanda section of Tokyo by a member of a right-wing organization called Shichisho Gidan and stabbed to death.The Central Committee of the Japan Communist Party posthumously conferred membership in the party on him.