"[1] As a lawyer, he served from 1931 as the chief of staff of the legal department under Hans Frank in the Party's Reichsleitung (national leadership) in Munich.

He was also a member of the presidium of Frank's Academy for German Law and of the National Socialist Association of Legal Professionals.

On 24 October 1939 Fischer became Chief Administrator (and in 1941 Governor) of the Warsaw District in the occupied General Government (the area of Poland that Germany did not formally annex) under Governor-General Hans Frank.

He was also responsible for terror in the occupied city, including mass executions, slave-labor pogroms and the deportation of Poles and Polish Jews to the various German concentration camps.

He was also responsible for the poor conditions in the temporary transit camp on the western outskirts of Warsaw in Pruszków, which the Nazis set up to intern people expelled from the capital.