Tahara graduated from Waseda University.
Tahara served as reporter of Asahi Shimbun (newspaper), took part in the social movement and became member of the Central Committee of National Farmers' Party and of the Social People's Party. He was elected member of the House of Representatives five times (since 1937).
After the war Haruji was elected chief of International Bureau of the Socialist Party but was purged. After being depurged, he became member of the Central Executive Committee of the Right-Wing Socialist Party, director of Organ Publishing Bureau and chairman of Japan Fishermen's Union.