On 23 January 1628, at the age of 13, August was appointed administrator of the Archbishopric of Magdeburg by its Chapter to replace the current holder of that title, Christian Wilhelm of Brandenburg. By that time, August had already served three years as coadjutor. Nevertheless, he could not assume his post: on 20 May 1631, after seven months of siege and plundering during the Sack of Magdeburg, the city was taken by the Imperial troops; the Catholic competitor for the diocese, Archduke Leopold Wilhelm of Austria, assumed the title of archbishop and administrator of Magdeburg. The Peace of Prague (1635) confirmed his rule over the city, but three years later, Swedish troops expelled the Habsburg army and restored August as administrator as of 19 October 1638. August finally took full control of Magdeburg on 31 December 1642 after a neutrality treaty was concluded with the Swedish general Lennart Torstenson. He was then able to begin the reconstruction of the city.