He developed a highly individual Romantic style of painting, in which richly colored, dappled, textured and glazed surfaces produce a scintillating effect. He painted courtly subjects inspired by Antoine Watteau; he also painted still lifes, portraits, and Orientalist subjects that owe much to the example of Delacroix.
After 1870, Monticelli returned to Marseille, where he would live in poverty despite a prolific output, selling his paintings for small sums. An unworldly man, he dedicated himself singlemindedly to his art.