After several years as a jewelry designer, D'Ylen became a full-time posterist in 1919 and signed an exclusive contract with Vercasson firm in 1922. He may have owed the job offer to the fact that he was a sincere admirer and disciple of Cappiello, who was the previous star at Vercasson, and thus the firm was assured of an uninterrupted flow of designs of unbridled exuberance. From the age of twelve, his special talents for design manifested themselves and in 1898, he won gold and silver medals from the Ville de Paris. After his regular studies, he was a pupil from 1900-2 at the Bernard Palissy School, a municipal school of Fine Arts, where he won many prizes, including one for jewelery design. He worked for a jeweler in the Rue de la Paix. He designed his first poster for the soap 'Erasmic' - a luminous figure of a woman in a soap bubble, on a background of green and pink. It was a resounding success. In 1914 he got married and joined the 279th Infantry Regiment. He then joined the Cartography Department of the Army. After the war, he quickly opted for a career in poster design. Vercassson were keen to sign him up and he joined the firm in 1919. They presented his work at the Salon de la Publicite. It was written that 'since Cheret, we have never seen such talent and Jean d'Ylen is really the master of the modern poster'. He had an exclusive contract with Vercasson for about thirty posters. He designed posters for Waterman, Ripolin, Jacquemaire, Shell, Bally and Sandeman's Port. The posters were on advertising hoardings all over the walls of France. Soon his creations were scattered over Europe, England (by Weiner), Sweden, Holland, USA, Canada and Australia. Widowed in 1924, he remarried in 1926, a beautiful young woman, by whom he had a daughter. From 1934, a dispute with Vercasson, led him to work directly for Weiner in London. He designed for Esso, BP, the Daily Herald, Power Ethyl and was widely recognized as a leader in his field. In 1938, he died prematurely, at the height of his career. His defining comment was in 1921, when he said, 'A poster must be expressive, colourful and have an attraction which captures the attention of a passer by'. Ninety of his works are held by the Bibliotheque Nationale and his daughter had a further twelve. Later a large collection of his work was found in an atelier in Paris. An exhibition of 72 of his posters was held at the Bibliotheque Forney at the Hotel de Sens in Paris in 1980.