That year, he joined the Munich law firm of Hans Frank, who regularly defended Adolf Hitler and the Nazi Party in court.

[1] Shortly after the Nazi seizure of power at the end of January 1933, Frank was appointed as the Minister of Justice for Bavaria on 10 March and Bühler became a member of his staff as a state attorney.

[2] In October 1934, after the process of Gleichschaltung (coordination) transferred sovereignty from the states to the central government, Bühler moved from Bavaria to become a prosecutor in the Reich Ministry of Justice in Berlin.

After the invasion of Poland by Nazi Germany in September 1939, Frank was appointed Governor General for the occupied Polish territories at the end of October and Bühler accompanied him to Kraków.

On 8 December, he was made head of the Governor General's office with the rank of Ministerialdirektor and, on 8 March 1940, he advanced to the position of State Secretary.

When his fellow conference participant Adolf Eichmann was asked at his 1961 trial in Israel what was meant by this statement, he answered that Bühler had wanted to intimate "that they should be killed".

[9] Shortly afterward, on 25 May 1946, in accordance with the Moscow Declarations that established the principle that war criminals were to be transferred for trial to the nations where their crimes took place, Bühler was extradited to the Polish People's Republic.

All were rejected by Polish President Bolesław Bierut, and Bühler was executed by hanging on 22 August 1948 at Montelupich Prison in Kraków.