He served as Ambassador Extraordinary to Poland (1752–56), was recalled at the outbreak of the Seven Years' War, was appointed Chevalier des Ordres du Roi (1757), Lieutenant-General (1760), Commandant of Franche-Comté (1761–62), then after the Peace, Governor of Saumurois (1770).

He is best remembered in connection with the Secret du Roi, the private—as distinct from the official—diplomatic service of Louis XV,[3] of which he was the ablest and most important member.

The Marquis organized the famous Diner de Metz (8 August 1775), when the young Marquis de La Fayette was convinced by the guest of honour, the visiting Duke of Gloucester, brother of King George III, that the insurgents' revolt in America was in some measure justified.

Broglie-Ruffec was involved with Beaumarchais in devising a scheme to offer secret support to the American Revolution in its early stages.

[4] His funeral monument is in the Angouleme Cathedral and a portrait of him, painted by Norman-Michel-Hubert Descours in 1762, is at the Château de Bourdeilles.