The title of duke of Mouchy was a French peerage held by members of a cadet branch of the Noailles family.
The founder of the branch, Philippe de Noailles (1715–1794), comte de Noailles, afterwards duc de Mouchy, was a younger brother of Louis, 4th duc de Noailles, and a more distinguished soldier than his brother. He served at Minden and in other campaigns, and was made a marshal of France on the same day as his brother. He was long in great favour at court, and his wife was first lady of honour to Marie Antoinette, and was nicknamed by her Madame Etiquette. This court favour brought down punishment in the days of the Revolution, and the old marshal and his wife were guillotined on 27 June 1794. He received the Spanish title of Prince de Poix in 1729, and that of duke of Mouchy, also a Spanish title, in 1747, when on the birth of his first son the title of prince of Poix became a courtesy title held by the heir.
Philippe Louis Marc Antoine, Duke of Noailles and Prince of Poix (1752–1819), was born on the 21st of November 1752. In 1767 he received the additional French non hereditary title of duke of Poix on the death of his older brother. In 1789 he was elected deputy of the States-General by the nobility of the bailliages of Amiens and Ham, but was compelled to resign in consequence of a duel with the commander of the Garde Nationale at Versailles. He left the country for some time, but returned to France and took part in the revolution of the 10 August 1792. He was for a time a member of the Constituent Assembly. He was, however, forced to quit the country once more to evade the fate of his father and mother. Returning to France in 1800, he lived quietly at his residence at Mouchy during the First French Empire. At the Bourbon Restoration he was brought again into favour and became a peer of France in 1817, when he was created duc de Mouchy. From that point, the head of the male line has been duc de Mouchy and prince-duc de Poix. He died in Paris on 17 February 1819.