Beseler was born in Greifswald, Pomerania. His father, Georg Beseler, was a law professor at the University of Greifswald. He entered the Prussian Army in 1868, fought in the Franco - Prussian War of 1870 - 1871, and had a successful military career until his retirement in 1910. Beseler was ennobled in 1904 by William II, German Emperor. He was recalled to active service and became commander of the third reserve corps in the German army when World War I broke out. In 1915 he was Military Governor of the German occupied part of Congress Poland and served as such until the end of the war.

In 1914 Beseler was brought out of retirement and was given command of the 3rd Reserve Corps in the German First Army led by Generaloberst Alexander von Kluck. The German Army took Brussels on 20 August, and the German command considered the Belgian Army defeated. The main force of the German armies marched toward France, leaving the 3rd Reserve Corps behind. Beseler was ordered to take possession of the city of Antwerp on 9 September. The Siege of Antwerp ended on 10 October, when the Antwerp Mayor, Jan De Vos, surrendered the city. Beseler followed the Belgian army and was halted in the Battle of the Yser.

In Spring 1915, Beseler was sent to the Eastern Front with Max von Gallwitz's 9th Army where he led the successful siege of Novogeorgievsk. On August 27, he was named Governor - general of Generalgouvernement Warschau, the zone of Polish lands under german military rule. Beseler hoped to gain three divisions for use by Central Powers from Polish volunteers, and to this end wanted to present a "facade of independent Poland". He also gave his support to the Polish Border Strip plan, which would see mass expulsions of Poles and Jews from territory annexed by German Empire from Russian held parts of Poland, and subsequent colonization of this area by German settlers.

Beseler reopened the University of Warsaw and the Warsaw Polytechnic Institute in November 1915 and allowed the usage of Polish at the University for the first time since 1869. Municipal councils were elected and the lower jurisdiction was organized by Polish locals. Despite these efforts, the German intentions were transparent and German rule was not tolerated by the Poles, while calls for Polish volunteers produced disappointing results; for the majority of Poles an Allied victory was seen as the best hope for genuine independence.

After the Act of 5th November of 1916, Beseler, now a full general, stayed and still wielded real power as the General Governor of the Government General of Warsaw, the German occupied part of the Kingdom of Poland, alongside the Austrian Governor General Karl Kuk, who resided in Lublin. He was also the titular commander of the so-called Polnische Wehrmacht. After the Act of 5 November was declared, he organized a ceremony in Warsaw's Royal Castle with such gestures as the unfurling of the Polish flag and the playing of the Polish national anthem; the event backfired as the Polish crowds started shouting "Out with the Germans!". On 4 October 1916 Beseler issued a decree allowing forced labour of Polish men aged between 18 and 45.

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 against the Poles and disliked in Poland for being too Prussian, Beseler died in 1921 in Neu-Babelsberg near Potsdam. He was buried at the Invalidenfriedhof in Berlin.

Beseler, besides many minor decorations, received the Pour le Mérite 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.