He was French Minister to United States from 1787 to 1789, and Ambassador Extraordinary to London in 1793. In 1769, he was posted to Lisbon with his brother, :fr:Gaspard Paulin de Clermont-Tonnerre|Marquis de Clermont d'Amboise as Attaché. In 1772, King Louis XV appointed him Minister-Counsellor to London. In 1776, he was appointed Secretary in the French Embassy at Naples, where his brother, Gaspard, was also serving. In 1778, he was appointed Minister Plenipotentiary to the Elector of Trier until 1783, when he was posted as a Special Envoy to London following the peace treaty signed between Britain and France. In 1787 he was appointed Minister Plenipotentiary to the United States. As minister he authored and the prospects for its ratification. In 1790, he was recalled to a diplomatic post in Berlin and in September 1791, King Louis XVI offered him the post of Foreign Minister, which he declined. Although denying accusations of organizing a coalition of counter-revolutionaries in Prussia, it later emerged that the Count had been the instigator of this anti-Republican coalition. The King of France, then appointed him as French Ambassador to Constantinople. The Revolutionary forces upon seizing power, called for the Comte to be guillotined. However, the King's brother, the futureLouis XVIII, gave :fr:De Moustier|de Moustier full authority to represent the interests of the French monarchy, and in 1792, he was granted the dignity of Regent, whilst the King remained in captivity. In 1793, he returned to England, where he conducted negotiations between British military commanders and Émigré troops. In 1795, he coordinated the landing of Royalists at Quiberon Bay. After the failure of the invasion, he fled to Prussia, then England before returning to France in 1814 upon the Bourbon Restoration, but was exiled again in 1815.
He was the third son of Philippe-Xavier, marquis de :fr:Mouthier-Haute-Pierre|Moustier by his wife Louise :fr:Château de Bournel|de Bournel, daughter of Jean-Charles, marquis de :fr:Namps-au-Mont|Namps. He married Antoinette-Louise Millet, who died in 1783; on 2 January 1779, in Koblenz, they had a son, Edward-Clement, who also went on to become a senior French diplomat. After the death of the marquise, Élie de Moustier became closely associated with her married sister, Anne-Flore Millet. His appointment as French Ambassador to the United States by Louis XVI caused further uproar in France, leading to his recall in October 1789. It became apparent that he had used his time visiting President Washington at Mount Vernon to paint portraits of George Washington and Eleanor Parke Custis. In 1801, he succeeded his elder brother Charles de Moustier in the marquessate.
