Born to a Jewish family in Tiraspol, on the eastern bank of the Dniester river (part of Imperial Russia at the time), he was the son of Alexandru Grünberg, a miller. In 1932, he joined the local section of the Romanian Union of Communist Youth, a wing of the Romanian Communist Party (PCdR); in 1933, due to his political activities, he was arrested and held for two weeks by the Romanian secret police, Siguranța Statului. Later in the 1930s, as associates of General Secretary Vitali Holostenco, he and Vasile Luca were elected to the internal Politburo (which was doubled by a controlling body inside the Soviet Union). In 1937, he joined the ranks of the Moscow-controlled PCdR. He did his military service in the Signals Regiment of Iași in 1937–39, being discharged with the rank of corporal. He subsequently worked for the telephone exchange in Chișinău.