He had four brothers, and his cousin Jean was Abbot of La Couture in Le Mans.

[1] Whilst serving as Archdeacon of Montfort, de la Forest was elected bishop of Le Mans on the death of his uncle in 1347, Pope Clement VI did not recognize the election, and appointed in his place Jean de Craon, Archdeacon of Passais.

[3] Pierre de la Forest was sent on two notable diplomatic missions during his career: to Avignon (1354) and to Bordeaux (1356).

[2] Pope Innocent VI invested Pierre de la Forest as cardinal during the consistory of 23 December 1356.

A statue of Pierre de la Forest was also placed in the choir.