Upon his father's death in 1346, Peter's elder brother, Charles, inherited the title of "Count of Alençon".

[citation needed] In 1361, Peter's elder brother, Charles III, Count of Alençon, renounced his counties[3] and became a Dominican friar, choosing Couvent des Jacobins de la rue Saint-Jacques in Paris.

Peter later moved his court to Argentan, as it was a fortified hilltop town about 15 miles (24 km) north of Alençon.

[6] Peter subsequently fought under Bertrand du Guesclin in Brittany; was wounded before Hennebont; and took part in an expedition against William I of Guelders in 1388.

[6] The couple had eight children, though their birth order is disputed:[Note 2] He also had one illegitimate son with Jeanne de Maugastel, Dame de Blandé, the wife of Pierre Cointerel, Count of Aunou-le-Faucon and Viscount of Perche under Peter:[10] In the 2021 film The Last Duel directed by Ridley Scott, he is portrayed by actor Ben Affleck.