Born in Bastia, Corsica to Antoine-Jourdan Piétri, a lawyer and préfecture councilman, and Clorinde Gavini, the daughter of a French National Assembly member.

[2] Piétri graduated from Collège Stanislas in 1899 and moved on to the École libre des sciences politiques for his university education.

During that time, he occupied a number of responsibilities, including: He remained involved in French politics during the Nazi occupation of France, becoming the Vichy ambassador to Spain from 1940 to 1944.

After the war, he was condemned in absentia to five years' indignité nationale by the High Court.

Avoiding politics after returning to France, he received the Académie Française's Grand prix Gobert in 1956 for his historical works.