In 1884 he met Claude Monet and Georges Seurat. He was struck by the systematic working methods of Seurat and by his theory of colors and became Seurat's faithful supporter, friend and heir with his description of Neo-Impressionism and Divisionism method. Under his influence he abandoned the short brushstrokes of Impressionism to experiment with scientifically juxtaposed small dots of pure color, intended to combine and blend not on the canvas but in the viewer's eye, the defining feature of Pointillism. Many of Signac's paintings are of the French coast. He loved to paint the water. He left the capital each summer, to stay in the south of France in the village of Collioure or at St. Tropez, where he bought a house and invited his friends.
Paul Signac, Albert Dubois-Pillet, Odilon Redon and Georges Seurat were among the founders of the Société des Artistes Indépendants. The association began in Paris 29 July 1884 with the organization of massive exhibitions, with the device "No jury nor awards" (Sans jury ni récompense). "The purpose of Société des Artistes Indépendants—based on the principle of abolishing admission jury—is to allow the artists to present their works to public judgement with complete freedom". For the following three decades their annual exhibitions set the trends in art of the early 20th century.
In 1886 Signac met Vincent van Gogh in Paris. In 1887 the two artists regularly went to Asnières-sur-Seine together, where they painted such subjects as river landscapes and cafés. Initially, Van Gogh chiefly admired Signac’s loose painting technique. In March 1889, Signac visited Vincent van Gogh at Arles. The next year he made a short trip to Italy, seeing Genoa, Florence, and Naples.
On 7 November 1892 Signac married Berthe Roblès at the town hall of the 18th arrondissement of Paris; witnesses at the wedding were Alexandre Lemonier, Maximilien Luce, Camille Pissarro and Georges Lecomte.
In September 1913, Signac rented a house at Antibes, where he settled with Jeanne Selmersheim-Desgrange, his mistress, who gave birth to their daughter Ginette on 2 October 1913. In the meantime Signac had left La Hune as well as the Castel Beranger apartment to Berthe: they remained friends for the rest of his life. On 6 April 1927, Signac adopted Ginette, his previously illegitimate daughter. His granddaughter, Françoise Cachin, was an art historian.