From September 1917 he took part with the Bavarian Infantry Battalion 702 (with Asia Corps) in the campaign in Palestine region of the Ottoman Empire.

After the war, Gürtner pursued a successful legal career, being appointed Bavarian Minister of Justice on 8 November 1922, a position he held until 1932.

During the 1924 Beer Hall Putsch trial, Hitler was allowed to interrupt the proceedings as often as he wished, to cross-examine witnesses at will, and to speak on his own behalf at almost any length.

After serving in the cabinets of Papen and Kurt von Schleicher, Gürtner was retained by Hitler in his post, and made responsible for coordinating jurisprudence in Nazi Germany.

The ill-treatment of prisoners at concentration camps in Wuppertal (Kemna), Bredow and Hohnstein (in Saxony), under the jurisdiction of local SA leaders, provoked a sharp protest from the Ministry of Justice.

Gürtner observed that prisoners were being beaten to the point of unconsciousness with whips and blunt instruments, commenting that such treatment reveals a brutality and cruelty in the perpetrators which are totally alien to German sentiment and feeling.

[8]On 2 October 1933, Gürtner was made a member of Hans Frank's Academy for German Law at its inaugural meeting.

[13] As a part of bid to retain a role for the judiciary in the repression of enemies of the state and to protect the Rechtsstaat, Gürtner opened the first session of the People's Court on 14 July 1934.

[16] In July 1935, Gürtner amended Paragraph 175 of the German penal code to extend its scope and increased the penalties.

By the end of 1935, it was already apparent that neither Gürtner nor Frick would be able to impose limitations on the power of the Gestapo, or control the SS camps where thousands of detainees were being held without judicial review.

During World War II, the feeble protestation of the Ministry of Justice was weakened still further, as alleged criminals were increasingly handled by the Gestapo and SS, without recourse to any court of law.

Gürtner provided official sanction and legal grounds for a series of repressive actions, beginning with the institution of Ständegerichte (drumhead courts-martial) that tried Poles and Jews in the occupied eastern territories, and later for decrees that opened the way for implementing the Final Solution.

A district judge and member of the Confessing Church, Lothar Kreyssig, wrote to Gürtner protesting (correctly) that the T4 program was illegal (since no law or formal decree from Hitler had authorised it); Gürtner promptly dismissed Kreyssig from his post, telling him, "If you cannot recognise the will of the Führer as a source of law, then you cannot remain a judge.