Duplessis was a goldsmith, bronze founder, sculptor and decorative designer in Turin before coming to Paris in c. 1740, where he may have been a pupil of Meissonier. He continued to work as a goldsmith and gilt-bronze founder in Paris, together with his son, while working for Vincennes and Sèvres where he was directeur artistique between 1748 and 1774. He became orfèvre du roi (a royal goldsmith) in 1758.
At Vincennes/Sèvres he supplied designs for new models, supervised the work of throwers, moulders and répareurs, advised on the placing of ground colours and on the outlines of reserves, and occasionally supplied gilt-bronze stands. His first recorded work was for a gilt-bronze stand for a bouquet of porcelain flowers in August 1748. In 1751 Louis XV commissioned the first major dinner service from Vincennes for which Duplessis supplied designs, and the models remained the chief dinner service shapes until the service made for Catherine the Great of Russia in 1778-9. He mainly designed vases, tea wares and useful wares. His name is often associated with new models in the stocklists and appears on drawings. Most of the shapes (especially the vases) of the 1750s are attributed to him, and some of the 1760s. His latest shapes are known from 1774, and he occasionally designed biscuit porcelain groups.
Duplessis also supplied the Paris dealer, Lazare Duvaux, with gilt-bronze mounts for Chinese porcelain vases. Designs known both in Sèvres and in gilt bronze could also be his work.