In 1937 he met David Seymour and Robert Capa, and did his first work for "Plaisir de France"; in 1938–39 he reported on a strike at Citroën and traveled in the Balkans. With Henri Cartier-Bresson, Ronis belonged to Association des Écrivains et Artistes Révolutionnaires, and remained a man of the left. In 1946 Ronis joined the photo agency Rapho, with Brassaï, Robert Doisneau and Ergy Landau, and was instrumental in forming the professional association Le Groupe des XV, and later joined Les 30 x 40, Club Photographique de Paris. Ronis became the first French photographer to work for "Life."