During his five years’ tenure of the last office he was mainly employed in provisioning the troops, who were suffering from the economic confusion resulting from John Law's system and the aftermath of the Mississippi Bubble.

He was the friend of Voltaire, who had been a fellow-student of his at the Jesuit college Louis-le-Grand, and a leading member of the Club de l'Entresol, an early modern think tank, the history of which he wrote in his memoirs.

France was at that time engaged in the War of the Austrian Succession, and the government had been placed by Louis XV virtually in the hands of the two brothers.

He dreamed of a "European Republic",[3] and wished to establish arbitration between nations in pursuance of the ideas of his friend the abbé de Saint-Pierre.

The generals negotiated in opposition to his instructions; his colleagues laid the blame on him; the intrigues of the courtiers passed unnoticed by him; whilst the secret diplomacy of the king neutralized his initiative.

He concluded the marriage of the Louis, the Dauphin to Maria, a daughter of King Augustus III of Poland, but was unable to prevent the election of the Francis, Grand-Duke of Tuscany as Holy Roman Emperor in 1745.

He then retired into private life, eschewed the court, associated with Voltaire, Condillac and d’Alembert, and spent his declining years in working at the Académie des Inscriptions, of which he was appointed president by the king in 1747, and revising his Mémoires.