Louis Charles Auguste Le Tonnelier Breteuil, Baron de (1730-1807), French diplomatist, was born at the chateau of Azay-le-Féron (Indre) on the 7th of March 1730. He was only twenty-eight when he was appointed by Louis XV. ambassador to the elector of Cologne, and two years later he was sent to St Petersburg. He arranged to be temporarily absent from his post at the time of the palace revolution by which Catherine II. was placed on the throne. In 1769 he was sent to Stockholm, and subsequently represented his government at Vienna, Naples, and again at Vienna until 1783, when he was recalled to become minister of the king's household. In this capacity he introduced considerable reforms in prison administration. A close friend of Marie Antoinette, he presently came into collision with Calonne, who demanded his dismissal in 1787. His influence with the king and queen, especially with the latter, remained unshaken, and on Necker's dismissal on the 11th of July 1789, Breteuil succeeded him as chief minister. The fall of the Bastille three days later put an end to the new ministry, and Breteuil made his way to Switzerland with the first party of émigrés. At Soleure, in November 1790, he received from Louis XVI. exclusive powers to negotiate with the European courts, and in his efforts to check the ill-advised diplomacy of the émigré princes, he soon brought himself into opposition with his old rival Calonne, who held a chief place in their councils.

After the failure of the flight to Varennes, in the arrangement of which he had a share, Breteuil received instructions from Louis XVI., designed to restore amicable relations with the princes. His distrust of the king's brothers and his defence of Louis XVI.'s prerogative were to some extent justified, but his intransigeant attitude towards these princes emphasized the dissensions of the royal family in the eyes of foreign sovereigns, who looked on the comte de Provence as the natural representative of his brother and found a pretext for non-interference on Louis's behalf in the contradictory statements of the negotiators. Breteuil himself was the object of violent attacks from the party of the princes, who asserted that he persisted in exercising powers which had been revoked by Louis XVI. After the execution of Marie Antoinette he retired into private life near Hamburg, only returning to France in 1802. He died in Paris on the 2nd of November 1807.

See the memoirs of Bertrand de Molleville (2 vols., Paris, 1816) and of the marquis de Bouillé (2 vols., Paris, 1884); and E. Daudet, Coblentz, 1789-1793 (1889), forming part of his Hist. de l'émigration.