Members of the Rohan family had filled the office of Bishop of Strasbourg since 1704, which made them princes of the Holy Roman Empire and the compeers rather of the German prince-bishops than of the French ecclesiastics.

Soon after taking orders, in 1760, he was nominated coadjutor to his uncle, Louis Constantin de Rohan-Rochefort, who then held the bishopric, and he was also appointed titular bishop of Canopus, Egypt.

Empress Maria Theresa was hostile to his intrigues; not only did he attempt to thwart her alliance with France, but as a vicar of the Church, he made little secret of his venal lifestyle.

[2] On the death of Louis XV in 1774, Rohan was recalled from Vienna, and coldly received in Paris; but his family's influence was too great for him to be neglected; in 1777 he was made Grand Almoner of France, and in 1778, abbot of St. Vaast.

Despite his enhanced status, the Cardinal was poorly received at court, having made himself an enemy of Queen Marie Antoinette, the daughter of Empress Maria Theresa, whose disapproval he had earned in Vienna.

Wishing to redeem himself in the eyes of the Queen, he got involved in the "affair of the diamond necklace" with the Comtesse de la Motte and others, including the notorious Cagliostro.