German statesman, leader of the Roman Catholic Centre Party, and twice chancellor during the Weimar Republic.

Marx studied law and rose from a judgeship to the presidency of the senate of the Court of Appeal at Berlin (1922). He founded and was first president of the Catholic Schools Organization (Düsseldorf, 1911) and he became president of the People's Union for Catholic Germany after World War I.

After joining the Centre Party, Marx served as a deputy in the Prussian Landtag (1899–1918) and the Reichstag (1910–32). From 1921 to 1928, he was the party's chairman and its leader in the Reichstag. He first served as chancellor from November 1923 until December 1924, during which time his government secured the acceptance of the Dawes Plan for war reparations payments. After a period as prime minister of Prussia (February–April 1925), Marx lost his bid for the presidency of Germany to Paul von Hindenburg. In May 1926, he returned as chancellor but resigned in 1928 after the successes of the Social Democrats. In December 1928 Marx resigned from the chairmanship of the Centre Party and withdrew from politics.