He was a pupil of Jean-Baptiste Descamps at the Rouen School of Fine Arts, then of Joseph-Marie Vien, where he had as classmates and friends Jacques-Louis David and François-André Vincent.

With a pleasing appearance, much natural wit and excellent recommendations he was soon admitted into the best society in the capital, especially in the salon of Marie Thérèse Rodet Geoffrin, who took a liking to him.

In this country of the arts, Lemonnier found a home full of kindness with the famous poet diplomat, Cardinal de Bernis, and devoted himself with enthusiasm to the study of masterpieces of the masters, from which he drew inspiration for the design and composition that is distinctive of his talent.

In Rouen he was charged, with his compatriot Charles Le Carpentier, to examine art works removed from suppressed religious institutions in the district and select those that should avoid destruction.

This painting exhibited at the Musée des Châteaux de Malmaison et Bois-Préau is an imaginary reconstruction of the salon of Marie Thérèse Geoffrin depicting, among others, the ministers Choiseul, Fontenelle, Montesquieu, Diderot and Marmontel, their hostess and a bust of Voltaire in a scene where the actor Lekain is reading Voltaire's play L'Orphelin de la Chine (The Orphan of China).