(22 September 1725 - 1 April 1802) was a French painter, known for the clarity and immediacy of his portraits.
He was born in Carpentras, near Avignon, into a family with an artistic bent and received his first training from his father, a surgeon and talented amateur, then with Joseph-Gabriel Imbert (1666-1749), who had been a pupil of Charles Le Brun. From 1744-47 or later he worked in Rome, in the atelier of Pierre Subleyras, who was also from the south of France, who died in 1749. In Italy Duplessis became fast friends with Joseph Vernet, another Occitan.
He returned to Carpentras, spent a brief time in Lyon then arrived about 1752 in Paris, where he was accepted into the Academie de Saint-Luc and exhibited some portraits, which were now his specialty, in 1764, but did not achieve much notice until his exhibition of ten paintings at the Paris salon of 1769, very well received and selected for special notice by Denis Diderot; the Academie de peinture et de sculpture accepted him in the category of portraitist, considered a lesser category at the time. He continued to exhibit at the Paris salons, both finished paintings and sketches, until 1791, and once more, in 1801.
His portrait of the Dauphine in 1771 and his appointment as a peintre du Roi assured his success: most of his surviving portraits date from the 1770s and 1780s. He received privileged lodgings in the Galeries du Louvre. In the Revolution, he withdrew to safe obscurity at Carpentras during the Reign of Terror. Afterwards, from 1796, he served as curator at the newly-founded museum formed at Versaillles, so recently emptied of its furnishings at the Revolutionary sales. His uncompromising self-portrait at this time of his life is at Versailles, where he died.