Mancini was educated at Lycée Louis le Grand before he joined the French Army serving in the Italian campaigns (1733) and in Bohemia (1740); but, he had to give up soldiering on account of weak health.

In 1738, he sold property including the château de Druyes to Louis Damas, Marquis of Anlezy.

He was subsequently French Ambassador to Rome (1748–1752), Berlin (1755–1756) and London, where he negotiated the Treaty of Paris (10 February 1763).

He regained his liberty after the fall of Maximilien Robespierre, and died in Paris on 25 February 1798.

In 1743 the Duke was elected to the Académie française for a poem entitled Délie, and from 1763 he devoted the greater part of his time to the administration of his Burgundian estates in Nevers as well as to Belles-lettres.