During the Weimar Republic era, he briefly served as Minister of Justice in the first cabinet of Hans Luther (from January to November 1925).

From 1899 he worked in the Prussian Ministry of Justice and in 1913 became Ministerialdirektor in the department for criminal cases and prison administration.

[1] From 1914 to 1916, Frenken served as Unterstaatssekretär (under secretary) at the German Ministry for Alsace-Lorraine.

He retired as a judge in 1922, but in January 1925 became Reichsjustizminister (Minister of Justice) in the first cabinet of Hans Luther as he was close to (or actually a member of) the Catholic Centre Party.

Frenken resigned on 21 November 1925, protesting the Locarno Treaties, which he had strictly opposed.