Born in Viroflay, Yvelines, he is the brother of scientists Axel Kahn and Olivier Kahn, and son of a Jewish father and a Catholic mother. Having obtained a degree in history, he started work at a postal sorting office, then at a printing works. He soon moved into journalism and was sent to cover the war in Algeria, undertaking the journalistic investigation that became known as the ‘Ben Barka affair’. Kahn then worked as a reporter for "Paris-Press", "L'Express" and Europe 1. He later moved to "Le Monde" as special correspondent for North Africa. In 1977, he became editor of the compilation of the ‘Nouvelles Littéraires’ and in 1983, was named editor of "Matin de Paris". In 1984, he created "L'Événement du Jeudi" then in 1997, together with Maurice Szafran, started the weekly magazine, "Marianne", where he was the editor in chief until 2007. He often writes under the pseudonym of François Darras or Serge Maury.