Although he was an admirer of Édouard Manet and owned paintings by Manet, Claude Monet, Edgar Degas and Berthe Morisot, his palette was more subdued than that of most of the Impressionists, and his technique more controlled. His style, between that of the conservative Paris Salon and Impressionism, has been called juste milieu, and he has been compared to Alfred Stevens, Giuseppe De Nittis, and James Tissot. Genre scenes depicting modern life included Au restaurant Le Doyen (1878) and Café sur la Terrasse (1890).
Portraits included Mme Duez (1877) and Alphonse de Neuville (1880).
Landscapes and seaside scenes were often inspired by the Normandy countryside around Villerville and Le Havre. In 1879 at the Salon he exhibited the large triptych Saint Cuthbert, depicting the stages of the life of Cuthbert set in landscapes based on the countryside around Villerville.
Considered his greatest work, it is now in the Musée d"Orsay. In 1883 Duez moved into a studio on boulevard Berthier, close to that of John Singer Sargent on the same street.
Duez"s circle also included the painters Paul-Albert Besnard, Jacques-Émile Blanche and Roger-Joseph Jourdain.
Duez carried out a number of commissions for the adornment of public buildings in Paris. These included Novembre and Décembre in the Palais Garnier"s Galerie du glacier, Virgile s’inspirant dans les bois (1888) for the Sorbonne, Louisiana Botanique and Louisiana Physique (1892) for the Hôtel de Ville"s Salon des Sciences, and L’heure de la tétée à la maternité (1895) for the Assistance publique - Hôpitaux de Paris. Duez died on 5 April 1896 from a cerebral haemorrhage while cycling in the Forest of Saint-Germain-en-Laye.