Austrian diplomat who, at the outset of the French Revolution, attempted to maintain the Austro-French alliance and to save the life of the Austrian-born French queen Marie-Antoinette.

Entering the diplomatic service in 1751, Mercy served at the Sardinian court, as ambassador to Russia, and, from 1766, as ambassador in Paris. An adviser to Marie-Antoinette, the daughter of Emperor Francis I and Maria Theresa of Austria, he was active on behalf of the French monarchy during the Revolutionary crisis of 1789–90, but he was recalled in 1790. After his efforts to save Marie-Antoinette from the guillotine had failed, he became political chargé d'affaires with the Austro-Prussian army in the Netherlands, and in July 1794 he became Austrian ambassador to London but died there shortly after his arrival.