Soble was born in 1903 as Abromas Sobolevicius, in then-Russian controlled Lithuania to a wealthy Jewish family. Soble travelled to Leipzig, Germany in 1921, to attend college, and where he joined the German Communist Party. In 1927, travelled to the Soviet Union, where he married and then returned to Germany. Soble studied briefly at the University of Berlin where he became a Trotskyist which led to his expulsion from the Communist Party and the university. Decades later, Soble would claim that he was coerced by Soviet agents to become a spy in 1931 after his wife returned to the USSR to visit her sick mother and threats to her safety were made if he did not cooperate. These claims are considered suspect as there is evidence that Soble had earlier contact with Stalin's agents.