Ernst Julius Waldemar Pabst (24 December 1880 – 29 May 1970) was a German soldier and political activist who was involved in extreme nationalist and anti-communist paramilitary activity in both the Weimar Republic and in Austria.

As a Freikorps officer, Captain Pabst gained notoriety for ordering the summary executions of Karl Liebknecht and Rosa Luxemburg in 1919 as well as for his leading role in the attempted coup d'etat by Wolfgang Kapp.

[5] Pabst permitted the summary execution of all individuals caught with a firearm, which resulted in the killing of many civilians and war veterans who were uninvolved in the strike.

[11] However Pabst would later claim that his initial intention had been for Liebknecht to be executed by firing squad as a German but for Luxemburg to be beaten to death by an angry mob as he felt her status as a Jew meant she deserved to die in a pogrom.

[14] Some of Pabst's lieutenants, including Horst von Pflugk-Harttung and Kurt Vogel, faced court martial for the killings although Pabst managed to ensure that his ally, Wilhelm Canaris, was in charge of proceedings and as a result the stiffest sentence handed down was the dismissal from service and two years imprisonment given to Vogel (whom witnesses had seen disposing of Luxemburg's body).

Research by Klaus Gietinger [de] on the trial of Luxemburg's murder has used the previously restricted papers of Pabst, held by the Federal Military Archives,[15] and concluded he had been central to the plotting and cover-up of this execution.

[18] However he was soon back in Germany, and became involved in the Nationale Vereinigung (National Union), a right-wing think tank formed by Wolfgang Kapp, Erich Ludendorff and others, and was central to the group's conspiracy to establish a rightist dictatorship.

[8] In July 1919, Pabst attempted to organise a coup, when he convinced his superior General von Hoffmann [de], the official commander of the Garde-Kavallerie-Schützen-Division, to march on Berlin in order to crush an alleged Communist uprising.

[21] In the immediate aftermath of the putsch, Pabst took refuge in Miklós Horthy's Hungary where he was soon joined by co-conspirator Walther von Lüttwitz.

[24] In Austria he linked up with the Heimwehr in Tyrol and played a central role in ensuring that the sometimes shaky dual leadership of Richard Steidle and Walter Pfrimer remained united.

[27] In this role Pabst was able to organise several disparate right-wing militia groups under the single Heimwehr banner, although he was ultimately unsuccessful in fully removing local differences from what remained an eclectic movement.

[29] Pabst was initially close to Johann Schober, and won his support in 1929, when he suggested repositioning the Heimwehr as a pro-government political party.

[37] Pabst's non-involvement in Nazism, given his history in the far right, raised some suspicions and rumours circulated that he had been in contact with Canaris and similar figures on the right of the German resistance.

Such rumours were never proven, but Pabst did leave Germany not long before the 20 July plot, and it has been suggested that he may have been aware that the attempt on Adolf Hitler's life was about to take place.