An SS-Gruppenführer in the Schutzstaffel (SS), he commanded German security police and intelligence services in Kraków, the Netherlands and northern Italy during the Second World War.

After an early release, he returned to Germany and was employed by the state government of Bavaria as a civil servant but was dismissed after a public outcry, though he retained his full pension.

On 16 October 1929, he joined the Kriminalpolizei (criminal police) in Stuttgart as a Regierungsassessor (government lawyer) in the German civil service.

[1] Following the Anschluss with Austria, Harster was made the commander of the state police regional office in Innsbruck from 31 March 1938 to 1 June 1940.

[2] Following the conquest of Poland in the Second World War, Harster served briefly as the Befehlshaber (commander) of Sicherheitspolizei (security police) and SD (BdS) for Kraków in November 1939.

He was briefly recalled to military service in the Wehrmacht in June 1940, during the Battle of France as a member of a machine gun company in the Gebirgsjäger (light infantry) Replacement Regiment 136.

He was directly involved in the Holocaust by rounding up and transporting an estimated 104,000 Dutch Jews, including Anne Frank, to extermination camps.

[4] He was found guilty and sentenced to 12 years imprisonment for his role in the persecution, deportation and murder of Dutch Jews and for his negligence in supervising the staff at the Amersfoort concentration camp.

[5] Upon release, Harster returned to Germany and obtained employment as a civil servant in Bavaria in 1956, becoming an Oberregierungsrat (senior government councilor) at the ministry of the interior.

In January 1966, he was arrested in Munich and was put on trial the following year alongside two of his closest aides Wilhelm Zoepf and Gertrud Slottke.