Born into a liberal Jewish family in Vienna, Hilferding became attracted to socialism while studying medicine, and he associated with various Marxists and socialists, including Otto Bauer (Bauer, Otto), Karl Kautsky (Kautsky, Karl), and August Bebel (Bebel, August). In 1906 he became an instructor in a training school in Berlin sponsored by the German SPD. The first volume of the Marx Studien series (1904–22), Böhm-Bawerk's Criticism of Marx, was his original contribution to Marxist thought. Responding to critics of Marx who held that the concentration of capital had not occurred in the way Marx expected, Hilferding's Finance Capital (1910) pointed to the role of banking and finance, arguing that the banks' increasing influence over industry led to monopoly and cartels and through them to economic imperialism and war. This work foreshadowed his role as the party's chief theorist and financial expert. He was political editor (1907–15) of Vorwärts (“Forward”), the main publication of the German SPD. At the outbreak of World War I he opposed war credits. Conscripted into the Austrian army, he served as a doctor on the Italian front. He acquired German citizenship in 1920 and became chief editor of Die Freiheit (“Freedom”), an organ of the Independent Social Democrats.

Hilferding was a Reichstag deputy from 1924 until he fled from Germany and the regime of Adolf Hitler (Hitler, Adolf) in 1933. The following year he drafted the Prague Program for exiled German Socialists. According to a dispatch from Berlin, he was found hanged in a Paris prison cell after his arrest by the French, who turned him over to the Nazis.