Konrad Haenisch (13 March 1876 - 28 April 1925) was a German Social Democratic Party politician and part of "the radical Marxist Left" of German politics. He was a friend and follower (Parvulus in his own words) of Alexander Parvus.
Haenisch was born in Greifswald, Province of Pomerania. He was a first-degree cousin of the famous German sinologist Erich Haenisch.
Haenisch became a socialist while at High School. His conservative family (his mother was a member of the House of Mecklenburg) took him out of school because of this and put him in a psychiatric institution. He escaped and fled to Leipzig where he started a career as a journalist and later editor for social democratic and socialist papers. During that time he became friends with Marxist celebrities like Rosa Luxemburg, Franz Mehring, Karl Kautsky, and especially Parvus, whom he regarded as mentor and friend during his whole life and also during later changes of his political direction.
Haenisch initially opposed World War I in 1914, but subsequently supported it. In a speech given to the 1916 SDP conference, he remembered the 'August enthusiasm':
He became famous, during World War I, as a member of the Lensch-Cunow-Haenisch group, a nationalist tendency within SPD which based the support of the SPD for the "war credits" in Reichstag on a Marxist theory suggesting that a German victory in World War I could be used by SPD, which was still a dominant force in European socialism, to transform Germany into a socialist state and to trigger socialist revolutions in the defeated countries. His associates in this movement were Heinrich Cunow and Paul Lensch, both former left-wing social democrats and Marxists close to Rosa Luxemburg.