[2] On 22 May 1712 he crowned Charles VI, Holy Roman Emperor as the King of Hungary and on 18 October 1714 also his wife Elisabeth Christine of Brunswick-Wolfenbüttel in St. Martin's Cathedral.

A Teutonic Knight, he converted to Catholicism in 1696 and became Provost of Cologne (1696–1725), then Bishop of Raab (1696–1725) and finally on 17 May 1706 was created a Cardinal by Pope Clement XI.

When the conversion was finally formalized, Christian August issued a certificate to the king, which was authenticated by the Papal nunzio.

On the occasion of the victory over the Turks in Belgrade in 1717 Christian August, as representative of the Emperor Charles VI, organized a magnificent celebration in the Imperial Diet realm.

The death of his brother Maurice Wilhelm, Duke of Saxe-Zeitz, on 15 November 1718 without surviving male issue, made him heir to the duchy of Saxe-Zeitz, but because he took the monastic vows (and the next in line to the inheritance, Christian August's nephew Maurice Adolf, was also a priest),[4] Zeitz was merged into the Electorate of Saxony in accordance with the will of Elector Johann Georg I.