Signac contributed annually to the Salon des Independants. He was the first non-Belgian member of the avant-garde Brussels Société des XX, with which he showed for some years. In Brussels in 1889, he supported Toulouse-Lautrec in his quarrel with a minor Belgian painter who had insulted Vincent van Gogh. With Seurat and van Gogh, Signac exhibited in Paris in 1887 at Le Théatre Libre.
After the death of Georges Seurat in 1891, Signac helped to list and classify his work and he actually headed the Neo-Impressionists. In 1892 he married Berthe Roblès, a relative of Pissarro and in 1893 they bought a house at Saint-Tropez, which was to become a resort and favourite of modern artists.
In 1892 he took part in a Neo-Impressionist group show. Among many exhibitions that he helped to organize were memorial shows for van Gogh and Seurat, in 1891 and 1892 respectively. In 1908 he became the president of the Société des Artistes Indépendants.
Signac himself experimented with various media. As well as oil paintings and watercolours he made etchings, lithographs, and many pen-and-ink sketches composed of small, laborious dots.
Watercolours form an important part of Signac's oeuvre and he produced a large quantity during his numerous visits to Collioure, Port-en-Bressin, La Rochelle, Marseille, Venice and Istanbul. The fluid medium allowed for more freedom than is found in his rather rigid oil paintings which are sometimes encumbered by the demands of theory. Colour being an important aspect of the artist's work, monochrome wash drawings such as Scène de marché are more rare. His methods in general were more precise and scientific than Seurat's, his paintings richer in colour and more luminous.
The neo-impressionists influenced the next generation; Signac inspired Henri Matisse and André Derian in particular, thus playing a decisive role in the evolution of Fauvism. As president of the annual Salon des Independants from 1908 until his death, Signac encouraged younger artists (he was the first to buy a painting by Matisse) by exhibiting the controversial works of the Fauves and the Cubists.
After 1900 Signac moved away from pointillism, opting instead for small squares of colour to create a mosaic-like effect, as in View of the Port of Marseilles, 1905, or The blessing of the tuna fleet at Groix, 1923. When he died in Paris in 1935, however, the style to which he dedicated himself had long ceased to be revolutionary.
Signac was untiring in his research and in his desire to expound his theories, and was extremely important as a writer on art. His book, From Delacroix to Neo-Impressionism (1899), a summary of the ideas and theories of the movement, is a standard text on the subject. He wrote an excellent study of Jongkind, a fine article on "The Subject in Painting" for a French encyclopedia, and other important articles and catalogue introductions.
By political views he was an Anarchist, as were many of his friends, including Félix Fénéon and Camille Pissarro.