As a member of the Academy of Inscriptions, he composed several memoirs on trial by combat, on the origin and revolutions of the Celtic and French languages, and on scenic representations and the ancient drama.

As a member of the Académie française, he assisted in compiling the new edition of the Dictionary, which was published in 1762; and he made some just and philosophical remarks on the Port Royal Grammar.

[2] The citizens of Dinan, whose interests he always supported with zeal, appointed him mayor of their town in 1744, though he was resident at Paris, and in this capacity he took part in the assembly of the estates of Brittany.

In 1763 he was advised to retire from France for some time, having rendered himself obnoxious to the government by the opinions he had expressed on the dispute between the duc d'Aiguillon, and M. de La Chalotais, the friend and countryman of Duclos.

The reputation of Duclos as an author was confirmed by the publication of his Considérations sur les mœurs de ce siècle (1751), a work justly praised by La Harpe as containing a great deal of sound and ingenious reflection.

The Mémoires pour servir à l'histoire du dix-huitième siècle, intended by the author as a sort of sequel to the preceding work, are much inferior in style and matter, and are, in reality, little better than a kind of romance.