Clemes Wenceslaus was the ninth child of the Saxon Elector Duke Frederick Augustus III, who was also the King of Poland. In 1760 he went to Vienna and entered the Austrian army as a field marshall. He was present at the Battle of Torgau (3 November 1760), but he decided that warfare was not for him and instead entered the church. In 1763 he was elected the Bishops of Freising and Regensburg, but he abandoned these dioceses for the Archbishopric of Trier and the Bishopric of Augsburg in 1768.