A former pupil at the Lycée Thiers [fr], Pietri entered the École normale supérieure in 1952 and obtained his agrégation d'histoire.
In 1975, he succeeded Henri-Irénée Marrou and held the chair of history of Christianity at the University Paris-Sorbonne.
[1] With his wife Luce Pietri, Jean-Marie Mayeur, André Vauchez and Marc Venard, Pietri initiated a monumental Histoire du christianisme des origines à nos jours, published from 1992 to 2001 at Éditions Desclée de Brouwer [fr] and meant to replace the Histoire de l’Église by Augustin Fliche.
He also directed, with Luce Pietri, the second volume of the Prosopographie chrétienne du bas-empire on Italy (2000), an endeavour started by Jean-Rémy Palanque and Henri-Irénée Marrou.
Pietri authored other works and articles fundamental to the historic understanding of ancient Christianity: