German socialist journalist and statesman who organized the Socialist Revolution that overthrew the monarchy in Bavaria (1918).

Eisner studied literature and neo-Kantian philosophy with Hermann Cohen (Cohen, Hermann) at the University of Marburg. In 1892 he published Friedrich Nietzsche und die Apostel der Zukunft (“Friedrich Nietzsche and the Apostle of the Future”). He began his journalism career by working on the Frankfurter Zeitung (1892–93); later he wrote for several Berlin journals and from 1898 was editor of Vorwärts, the official paper of the Social Democratic Party (Social Democratic Party of Germany). After Eisner became a Bavarian citizen, he worked as a freelance writer in Munich.

In 1914 he opposed German aid to Austria-Hungary against Serbia. During the early stages of World War I, however, Eisner supported the government; but in 1917, influenced by pacifist principles, he joined the Independent Social Democratic Party (USPD) of which he later became a leader. Eisner was arrested in 1918 as a strike leader but was shortly released and resumed his leadership of the USPD. In November 1918 he successfully organized a revolution that overthrew the monarchy, proclaimed the Bavarian Republic, and demanded peace. Eisner became first prime minister and minister of foreign affairs of the new republic. He strove to bring about internal security, to reconcile and unite the various socialist parties in Bavaria, and to effect economic and social reform. In February 1919 he was assassinated by a zealous reactionary student.

Eisner's collected works were published in two volumes in 1919.