After attending a school in Oels, Prittwitz joined the 3rd Guard Grenadier Regiment and fought in the Austro-Prussian War. He was then commissioned as a junior officer in the 38th Fusileers with which regiment he served in the Franco-Prussian War. After attending the Prussian Military Academy Prittwitz was appointed to the 6th Jaeger Battalion.
Prittwitz enjoyed rapid promotion and a brilliant career: brigade commander in 1897, divisional commander four years later, and head of the XVI Army Corps at Metz in 1906. He was promoted colonel general one year before the Great War broke out and appointed inspector general of the First Army Inspectorate. Among his troops he enjoyed the unflattering nickname of "the rotund soldier."
In August 1914, Prittwitz was entrusted with command of the Eighth Army for the defense of East Prussia. His job was to secure this historical province against the so-called Russian steamroller and, if possible, to lend assistance to the Austro-Hungarian offensive in Galicia. Above all, Prittwitz was to tie down as many Russian forces as possible while the main German thrust would be directed at Paris; once the French had surrendered, succor was promised Prittwitz.
Initially, all went according to plan. On August 17 General Hermann von François, one of Prittwitz's commanders, seized the initiative and attacked the Russians near Stalluponen. Unfortunately, this bold move encouraged Prittwitz three days later to launch a frontal assault against the Russians near Gumbinnen. Vastly outnumbered by General Rennenkampf's Niemen Army, Prittwitz panicked at the first repulse and broke off the engagement. Worse, he called military headquarters at Koblenz and informed General Helmuth von Moltke that he would have to abandon East Prussia to the Russians, retreat behind the Vistula, and possibly surrender even the Vistula fortresses unless reinforcements arrived at once.
Prittwitz's precipitate action had been caused, in part, by the unexpectedly rapid deployment of General Samsonov's Narev Army on Prittwitz's southern flank near Neidenburg. In his haste, Prittwitz had not bothered to inform his staff of his call to Moltke. In fact, Lieutenant Colonel Max Hoffmann within hours managed to persuade his commander to face the Russian challenge and to deal with Samsonov by shuttling troops south from Gumbinnen the very plan that was to result in victory at Tannenberg a few days later. However, on August 22 Prittwitz received a curt telegram announcing that a special train was on the way with the new commanders for the east: Generals Paul von Hindenburg and Erich Ludendorff. Thus ended his career as a result of indecision and half-measures. Prittwitz died a broken man in Berlin on March 29, 1929.
On 19 May 1874 Prittwitz married Olga von Dewitz (30 August 1848 – 9 January 1938), the daughter of Kurt von Dewitz, a landowner and his wife Euphemia, née von der Groeben. Their only son died 23.5.1918.