Some of his ancestors were of German-Bohemian ethnic descent and had assimilated into Czech society. From 1906 he worked as a police official for police in Prague and in January 1918 he even became a clerk in the Presidium of the Police in Prague. During World War I Bienert cooperated closely with the Czech resistance movement and after the proclamation of Czechoslovak independence in October 1918 he was rewarded with an appointment to the position of Prague Police Director.