Following
Austria's Anschluss with
Nazi Germany on 12 March 1938, Uiberreither was promoted to SA-
Brigadeführer and was named Acting Police President for Graz. At the
parliamentary election of 10 April, he was elected as a Nazi deputy to the
Reichstag from the newly renamed
Ostmark. On 24 May 1938,
Adolf Hitler appointed him
Gauleiter of Gau Styria. Additionally, on 9 June he was named
Landeshauptmann of
Styria, thus uniting under his control the highest party and governmental offices in his jurisdiction. On 1 October 1938, Uiberreither officially joined the Nazi Party with membership number 6,102,560. On 9 November of the same year, he was advanced to the rank of SA-
Gruppenführer. In May 1939 Uiberreither married Käte Wegener (1918–2012), the daughter of
Alfred and Else Wegener. They had four sons. In October 1939 he entered
military service as a mountain trooper (
Gebirgsjäger) with the
3rd Mountain Division and participated in the German landings in
Norway. He was awarded the
Iron Cross, 2nd class and the
War Merit Cross, 1st and 2nd class. In July 1940, he was discharged from the
Wehrmacht with the rank of
Leutnant in the reserves. On 1 April 1940, a new more centralized administrative structure went into effect in Austria. The federal States were abolished and the country was divided into seven
Reichsgaue, each headed by a
Reichsstatthalter (Reich Governor) reporting directly to Hitler. Uiberreither was appointed
Reichstatthalter of
Reichsgau Styria. On 14 April 1941, after the conquest of
Yugoslavia, he was named the
Chief of Civil Administration in the occupied area of
Lower Styria (now part of
Slovenia). This was an area of 6,050 square kilometers with a population of approximately 530,000. Uiberreither was given a mandate by Hitler to "Make this territory German again for me." Accordingly, Uiberreither oversaw a policy of ruthless
Germanization. He convened a meeting on 6 May 1941 at
Maribor to plan measures that resulted in the expulsion to
Serbia of tens of thousands of
Slovenes in three waves beginning in July 1941. The Slovene language was banned and place names were Germanized. These repressive actions led to increased
partisan attacks upon German occupation authorities and their local collaborators. In addition, the
Aktion T4 program of
euthanasia involving mentally impaired individuals was operational within Styria and Lower Slovenia at this time. It is estimated that over 500 patients from various mental care facilities were gassed to death at the
Hartheim Euthanasia Center near
Linz. Also, 62 children and teenagers were killed at the Fendhof hospital in Graz. On 30 January 1939, Uiberreither was awarded the
Golden Party Badge. On 16 November 1942, he was appointed the
Reich Defense Commissioner for his
Reichsgau. On 9 November 1943, he was promoted to SA-
Obergruppenführer. In September 1944 he became the leader of the
Volkssturm in Styria, a last-ditch Nazi Party militia set up towards the end of the
Second World War and associated with the Nazi "
Werwolf" organization. This consisted of conscripted males between the ages of 16 and 60 who were not already in the military. Uiberreither was also charged with construction of defensive positions against the anticipated assault by the
Red Army, which involved the procurement of forced civilian labor. ==Postwar life==