Arthur Greiser joined the Nazi party and SA in 1929 and the SS in 1931. He was the Senate President (Senatspräsident) of the Free City of Danzig (1935–1939) and the administrator (Reichsstatthalter und Gauleiter) of Reichsgau Wartheland (1939–1945).
Greiser typified the brutality exhibited by officials of Nazi Germany to the Poles. He was an ardent racist who enthusiastically persued an 'ethnic cleansing' program to rid the Warthegau of Poles and to resettle the 'cleansed' areas with ethnic Germans. This was along the lines of the racial theories espoused by SS Reichsführer Heinrich Himmler. Mass expulsions of Poles from the Warthegau to the General Government and summary executions were the norm.
After the war, the Poles tried him for war crimes. He plea that he was only following orders did not hold up as it was shown that other Gauleiters did not follow a similar policy (such as Albert Forster in the other German-annexed section of Occupied Poland called Danzig-West Prussia, who simply declared the Poles in his area of responsibility to be Germans). After Greiser was convicted, he was paraded around the city of Poznan in a cage, before being hanged.