Élisabeth (nickname, "Isabelle") Bourdeau de Fontenay is the daughter of Henri Bourdeau de Fontenay, from a right-wing Catholic family, a lawyer who supported the Front Populaire and an early Resistance fighter, and Nessia Hornstein, a dentist of Jewish origin but converted to Catholicism, whose family had fled Odessa during the Odessa pogroms of 1905.

[2] Élisabeth was raised Catholic, baptized as a child, then enrolled at the age of five at the Collège Sainte-Marie in Neuilly-sur-Seine.

At the age of 22, she abandoned Catholicism and turned to Judaism; she details her conversion in the book Actes de naissance (Birth certificates), published in 2011.

From September 2010, Fontenay presented, with Fabienne Chauvière, a program dedicated to animals on France Inter: Vivre avec les bêtes (Living with the beasts).

In 2018, she prefaced the book Le Nouvel Antisémitisme en France, a collective of texts by Luc Ferry, Pascal Bruckner, Philippe Val, Boualem Sansal, Éric Marty, Georges Bensoussan, Jean-Pierre Winter, Daniel Sibony, Barbara Lefebvre [fr], Monette Vacquin, Michel Gad Wolkowicz, Noémie Halioua, Jacques Tarnero, Caroline Valentin, and Lina Murr Nehmé.