Political and party activist, publicist. He received a full Jewish religious education and – according to some accounts – passed the examinations allowing him to become a rabbi. At the same time he was already, as a young man, taking part in the revolutionary movement. From 1904 he was a Bolshevik. He worked in illegal presses in Vilno and Moscow, and played an active part in the revolutionary events of 1905–1907. In 1909 he was arrested and sentenced to four years' imprisonment, followed by exile to Siberia. In 1913 he fled to France. In 1917 he returned to Russia and took part in the work of the Communist Party. In 1918 he became Stalin's deputy in the people's commissariat for nationalities and head of its Jewish section; he also edited the Yiddish-language newspapers "Di Varkhayt" and "Der Emes". He was a constant and uncompromising supporter of the Zionist movement and of BUND. He took part in the liquidation of all forms of independent Jewish national life, and called not only for the banning of the Jewish communes' activities, but also for the cessation of the work of Jewish periodicals, Hebrew-language theatres and Jewish educational institutions; he advocated full "Yiddishisation". He is alleged to have said that "in Hebrew, even the Interrnationale sounds counterrevolutionary." During the 1920s he was involved in Party work in Belorussia and Ukraine, and was head of the national sector of the Central Committee of the Communist Party. From 1930 he was director of the Nationalities Institute in the USSR's Central Executive Committee. Dimanshtein was chairman of OZET and founded, on the orders of the Central Committee, the Jewish National Region at Birobidzhan. He perished in the Stalinist repressions.