A founding member of the NSDAP in 1921; after the re-establishment of the party, he rejoined in 1925 and quickly became one of Adolf Hitlers favourites. He was appointed Gauleiter of the Gaus Rheinland and Ruhr in 1922-29, then Gauleiter of Hamburg in 1929, a post he was to hold until 1945. He was also member of the German Reichstag. After Hitler gained power on 16 May 1933, Kaufmann was appointed Reichsstatthalter (Regional Governor) of Hamburg with absolute power over some 1.8 million people. One of his first acts was to turn over control of the citys Fuhlsbüttel Prison to the SA and SS, where it quickly became the nucleus of the notorious Kola-Fu concentration camp.
In September 1941, after Allied bombing of Hamburg had rendered many people homeless, Kaufmann petitioned Hitler to allow him to deport local Jews so that he could confiscate their property to rehouse bombed-out citizens. Hitler quickly responded, allowing Kaufmann the dubious distinction of being the first Nazi leader to deport German Jews, in this instance to the ód Ghetto in Poland.