Over the course of his career, urban sociologist Paul-Henry Chombart de Lauwe evolved from a sociological interpreter of human needs into an advocate of the democratization of city planning. The major factors shaping this trajectory were his contacts with liberal Catholic associations, his education under ethnologist Marcel Mauss, his teaching experience at the École des cadres d'Uriage, and his own studies of working-class communities. Chombart de Lauwe took French urban sociology in novel directions and effected an important and underappreciated liberalization of city planning. Analysis of Chombart de Lauwe also challenges recent trends in the historiography of the Catholic Left.