From 1775 onwards he became one of the main art dealers and painting experts in Paris, specialising in restoring old masters, particularly Dutch ones, and publishing catalogues of them for commercial purposes.

They had one child, Jeanne Julie Louise Lebrun, who in 1800 married Gaëtan Bertrand Nigris, director of the Imperial Theatre in Saint Petersburg.

[5] In 1781 he and his wife travelled to Brussels to buy works at the sale of the fallen governor Prince Charles Alexander of Lorraine.

The following month, Le Brun bought several paintings for the Louvre with Jacques-Louis David's support but without the government's knowledge, including a Holy Family attributed to Rembrandt and Peter Paul Rubens' Portrait of Suzanne Fourment.

His purchases totalled 30,000 livres at a time when the First Republic was in a budgetary crisis and so an annual acquisitions budget was set for the Louvre to avoid a repeat of the situation.

He failed to return to the Parisian art market, pushing him into debt, and on 14 January 1807 he was forced to sell the Salle Le Brun and the mansion to his ex-wife, an excellent business-woman.