In 1704 he married a niece of the tavern-keeper Procope, whose house in Paris was a meeting-place for artists and intellectuals. The following year Grimou was approved (agréé) by the Académie Royale de Peinture et de Sculpture. Although instructed by the Académie to paint as his morceaux de réception portraits of the sculptor Jean Raon (1630–1707) and the painter Antoine Coypel, he failed to present either picture and in 1709 the agrément was annulled. As a result he joined the Académie de St Luc.
Grimou was probably a pupil of François de Troy, from whom he learnt to use a palette of unusually warm colours and to work with uncomplicated pictorial formats (e.g. Woman with a Fan, 1711; see sale cat., Paris, Hôtel Drouot, 27 April 1983, no. 23). Certain audacities in his handling, however (e.g. Man Wearing a Cuirasse, 1728; Orléans, Musee Beaux-Arts), place him well into the 18th century. Grimou’s portraits, often intimiste works, comprise his known oeuvre; their significance for the development of early 18th-century French art has hitherto not been fully appreciated. Many of them are half-lengths, and they clearly provoked the fantasy portraits later sketched by Jean-Honoré Fragonard, who, moreover, painted pastiches of Grimou’s manner (e.g. Portrait of a Girl, London, Dulwich Picture Gallery). Grimou’s influence can also be discerned in the work of Charles Eisen, Joseph Ducreux and Jean-Baptiste Greuze. For this reason it can be said that by introducing into France northern formulae for improvised portraits, Grimou played a role not unlike that of Antoine Watteau, who was responsible for introducing the fête galante into French art. Grimou’s success was such that he often repeated the same types, the best known being the Young Male Pilgrim and Young Female Pilgrim (both 1725; Florence, Uffizi), which he conceived as pendants—a successful commercial formula of that period. He introduced relaxed poses, informal costume and a light-hearted symbolism based on music and wine. Examples include the Young Man Playing a Recorder (1716), which appears on the cover of Figaro illustré (1906), the Hurdy-Gurdy Player with a Boy Playing a Recorder (1727; see sale cat., Paris, Hôtel Drouot, 25 March 1985, no. 25), the Young Woman Playing a Hurdy-Gurdy (1728; see Art at Auction, vii, March 1985, p. 7) and the Happy Drinker (1729; Paris, Louvre). Grimou also painted many self-portraits on the same themes: Self-portrait as a Drinker (1724; Paris, Louvre), Self-portrait as Bacchus (1728; Dijon, Museum Magnin) and other personal likenesses that depended on the same symbolic references. Nevertheless he did not scorn to use more traditional formats from time to time, for example in his portrait of the Marquis de Sourches (1723; see Gabillot, p. 315), and occasionally he painted allegorical portraits, such as the Woman and Child (1727; Béziers, Musee Beaux-Arts).
In terms of style as well as iconography, Grimou was influenced by Dutch 17th-century masters, notably Rembrandt van Rijn, almost to the point of pastiche, and because of this he was often confused with his contemporaries Jean-Baptiste Santerre and Jean Raoux. The many anecdotes concerning Grimou, though distortions of the truth, reveal how, from a very early stage, critics felt the need to discuss a type of painting that was hard to praise but the success of which forced it to be noticed.
Grimou is represented in the following collections: Hermitage, St Petersburg; Accademia Carrara, Bergamo, Italy; Musée des Augustins, Toulouse, amongst others.