During the war he became a senior official in the occupation government of the Soviet Union, achieving the rank of Generalkommissar for Generalbezirk Weißruthenien.

When in 1933 the Nazis came to power he remained active in the German Christian movement which sought to "Nazify" the 28 Protestant church bodies in Germany.

In late 1935 the Supreme Party Court under Chairman Walter Buch, the father-in-law of Martin Bormann, began an investigation into Kube due to allegations of adultery and corruption in running his Gau, including nepotism, favoritism and a dictatorial management style.

[7] On 17 July 1941, in the wake of the German occupation of the western parts of the Soviet Union, he was appointed Generalkommissar for Weissruthenien (now known as Belarus), with his headquarters in Minsk.

With indescribable brutality on the part of both the German police officers and particularly the Lithuanian partisans, the Jewish people, but also among them Belarusians, were taken out of their dwellings and herded together.

The Belarusians were in greatest distress to free themselves from the encirclement.The letter concluded: I am submitting this report in duplicate so that one copy may be forwarded to the Reich Minister.

To bury seriously wounded people alive who worked their way out of their graves again is such a base and filthy act that the incidents as such should be reported to the Führer and Reichsmarschall.

During a search by German and Belarusian police, a group of children were seized and thrown into pits of deep sand to die.

On 31 July he wrote to his friend, the Reichskommissar for the Ostland, Hinrich Lohse, in Riga: Following lengthy talks with the SS-Brigadeführer Zenner and the extraordinarily diligent head of the SD, SS-Obersturmbannführer Strauch, in the last two weeks in White Russia we have liquidated roughly 55,000 Jews....In the city of Minsk about 10,000 Jews were liquidated on 28 and 29 July.

The bomb was placed by Soviet partisan Yelena Mazanik (1914–1996), a Belarusian woman who was hired in Kube's household as a maid and was convinced to assassinate him later.

According to alternate version, the explosives were set up by Lev Liberman from the Minsk ghetto, who was also employed in the household, but this later proved to be false.

Owing to Kube's antagonistic attitude to some SS anti-Jewish actions, Himmler felt that the dead man had been well on the way to booking himself a place in a concentration camp anyway,[14] and reportedly described the assassination as a "blessing".

On 29 October 1943 she was awarded the title Hero of the Soviet Union, along with other members of the assassination group Nadezhda Troyan and Mariya Osipova.