[1] At the outbreak of World War I in 1914, Beseler was brought out of retirement and given command of the 3rd Reserve Corps in the German First Army led by Generaloberst Alexander von Kluck.

On 27 August 1915[2] Beseler was made Military Governor of the German-occupied part of the zone of Polish lands, or Congress Poland, and served as such until the end of the war.

Beseler hoped to assemble three divisions of Polish volunteers for use by the Central Powers, and to this end wanted to present a "facade of independent Poland".

[8][9] After Poland declared independence on 11 November 1918 and all German soldiers in Warsaw were disarmed, Beseler fled in disguise to Germany.

A broken and disillusioned man, attacked by the German Conservatives and Nationalists as having been too liberal towards the Poles, but disliked in Poland for being too Prussian, Beseler died in 1921 in Neubabelsberg near Potsdam.

Beseler, besides many minor decorations, received the Pour le Mérite with oak leaves and the Iron Cross (1st and 2nd Classes), and was a Commander with Star and Crown of the Prussian Order of the House of Hohenzollern.