He joined the Nazi Party in 1922 and the "Schutzstaffel" (SS) in 1931. Appointed Higher SS and Police Leader (HSSPF) of Danzig and Westpreussen in September 1939. In October 1939, he ordered the murder of 1,400 mentally disabled people and inmates in Pomerellen and another 2,000 mentally disabled people from the Irrenanstalt Konradstein. Hildebrandt from 1943 until his capture after the war in 1945, led the SS Race and Settlement Main Office ("SS-Rasse und Siedlungshauptamt"; RuSHA). He held the rank of SS-"Obergruppenführer". He was convicted in the phase of the Nuremberg trials known as the RuSHA Trial, for measures put into force in the furtherance of the "germanization" component of the Generalplan Ost program in the Danzig-West Prussia area. This involved the resettlement of Germans in the Nazi occupied territory after the forced displacement and deportation of the native families from those lands. As RuSHA chief, he was also responsible for conducting the official Race test on the population of the occupied territories for racial selection. After the war, he was convicted of war crimes and executed.