The son of a colonial supply trader, Köhler was born in Weinheim, attended Volksschule there until 1906 and left the Realgymnasium in his hometown in 1912 after earning his Abitur.

At the beginning of the First World War he entered the Imperial German Army as a one-year volunteer in Reserve Infantry Regiment 109 and was deployed on the western front from October 1914.

Awarded the Iron Cross, 2nd class, Köhler returned to Weinheim after the end of the war, where he initially worked in his parents' store.

In addition, Köhler was a member of the Deutschvölkischer Schutz- und Trutzbund, the largest and most influential antisemitic organization in Germany at the time.

After the Nazi seizure of power at the national level, they began the process of taking control of the independent state governments.

Köhler, in his capacity as acting Gauleiter, on 6 March 1933 issued an ultimatum demanding the resignation of the Baden state government.

Following Wagner's appointment to the newly-created position of Reichsstatthalter (Reich Governor), Köhler on 6 May 1933 succeeded him as Minister President of Baden, as well as head of the combined Ministry of Finance and Economics.

Towards the end of the war, Köhler was in Karlsruhe and refused Gauleiter Wagner's order to leave the city in view of the approaching French army.

In the Third Reich, Köhler ultimately functioned without any problems in his area of responsibility and thus made a significant contribution to supporting and consolidating the Nazi regime.