An anaesthetist and hospital practitioner since 1997, in 1971 he was the co-founder of Médecins sans Frontières, of which he was Chairman and Honorary Chairman for 15 years. From 1998 to 1992, he was head doctor at the Fleury Merogis (Essonne) detention centre. In 1993, he founded Samusocial de Paris, which he still chairs today, before joining the government as Secretary of State for Emergency Humanitarian Action from 1995 to 1997. In 1998, he established Samusocial International, which he currently chairs.

He also presides over numerous other organizations he has helped to create, including the High Commission for the Accommodation of Disadvantaged People since 1997, the Groupement d'Intérêt Public Traces de Pas since 1999, the Maison Ouverte association since 2003, and the Fondation Médéric Alzheimer since 1999.

He has published a large body of work, including essays related to his experiences and his analyses of emergency situations and exclusion.