After the Nazis seized power in 1933, he managed within a very short time to rise high in the ranks from a prosecutor to President of the People's Court (Volksgerichtshof).

The groundwork on which this rise was built was not merely that Thierack had been a Nazi Party member, but rather also that he had been leader of the National Socialist jurists' organization, the so-called Rechtswahrerbund.

He introduced the monthly Richterbriefe in October 1942, in which were presented model – from the Nazi leaders' standpoint – decisions, with names left out, upon which German jurisprudence was to be based.

When he became Reich Minister of Justice in August 1942, Thierack saw to it that the lengthy paperwork involved in clemency proceedings for those sentenced to death was greatly shortened.

[2][3] At Thierack's instigation, the execution shed at Plötzensee Prison in Berlin was outfitted with eight iron hooks in December 1942 so that several people could be put to death at once, by hanging (there had already been a guillotine there for quite a while).