He entered the diplomatic service of
Austria in
Paris in the train of
Reichsfürst Wenzel Anton of Kaunitz-Rietberg. He became Austrian ambassador in
Turin at the court of King
Charles Emmanuel III of Sardinia, in
St. Petersburg at the court of
Catherine the Great, and then
Austrian ambassador in Paris at the court of King
Louis XV in 1766. In Paris, his first work was to strengthen the
Franco-Austrian alliance, which was cemented in 1770 by the marriage of the
Dauphin, afterwards
Louis XVI, with Archduchess Maria Antonia Josepha Johanna of Austria, youngest daughter of Empress
Maria Theresa, afterwards known as Queen
Marie Antoinette. When Louis and Marie Antoinette ascended the throne of France in 1774, Mercy-Argenteau became one of the most powerful personages at the French court due to his influence over Marie Antoinette, which made her unpopular with the French nobility and French people. He was in Paris during the turbulent years that led up to the
French Revolution, and gave powerful aid to the finance ministers
Étienne Charles de Loménie de Brienne and
Jacques Necker. In 1792, he became governor-general of the
Austrian Netherlands, where the
Brabant Revolution had just been suppressed by Austria. There, his ability and experience made him a very successful governor. Although at first in favour of moderate courses, Mercy-Argenteau supported the action of Austria in making war upon its former ally after the outbreak of the
French Revolution, and in July 1794, he was appointed Austrian ambassador to
Britain, but he died a few days after his arrival in London. ==Private life==