Hadjadj was born in Nanterre to Jewish parents of Tunisian heritage. In his teens he was an atheist and anarchist, and he maintained a nihilistic attitude for most of his twenties until, in 1998, he converted to Catholicism. His book Réussir sa mort: Anti-méthode pour vivre, won the Grand Prix catholique de littérature in 2006. Currently Hadjadj teaches philosophy and literature in Toulon. He is married to the actress Siffreine Michel. They have four daughters and two sons. In 2014, Hadjadj was nominated as member of the Pontifical Council for the Laity.