In March of 1933, he was appointed Mayor of Munich and held that post until the end of World War II in Europe. During his time as mayor, Fiehler was zealously anti-Semitic and saw to it that the Jewish population of the city was persecuted. After the war in January 1949, Fiehler was sentenced to two years in a labour camp, but the sentence was suspended given the previous three and a half years of detention he had already served.