Grossman earned his Juris Doctor in 1908 from the Jagiellonian University. At the end of 1908, he went to the University of Vienna to study with the Marxian economic historian Carl Grünberg, withdrawing from his leadership role in the JSDP (although he remained on its executive until 1911 and had contact with the small JSDP group in Vienna, the Ferdinand Lassalle Club). With the destruction of the Austro-Hungarian empire at the end of World War I, Grossman became an economist in Poland, and joined the Communist Party of Poland.