Possidius is mainly known for his description of the life of Augustine. Details of his own life are not plentiful.
Possidius was a convert from paganism.
It would seem that the association of Possidius with Augustine began about the year 390 in the monastery for men that Augustine established in Hippo.
In his Life of Augustine, Possidius wrote, "I lived in close friendship with him for forty years."
He attended the African church councils of his day, and twice travelled to Italy to defend the church.
Along with Augustine and Alypius, Possidius was among the seven Catholic bishops chosen to represent the 266 Catholic bishops of the region at the famous debate in Carthage between the Catholics and the Donatist heretical church in the year 411 A.D.
Possidius became Bishop of Calama (a town later renamed Guelma) in Numidia, North Africa, in or about the year 397.
He seems to have established a monastery there, after the example of Augustine.
There he suffered a grievous persecution from heathens and Donatists. For the letters between Possidius and Augustine, it is known that in 403 while he was bishop of Calama, Possidius suffered a serious physical assault at the hands of the local Donatist bishop, Crispin, and some of his clerical followers.
Alypius was obliged to leave his city for some time, and on one occasion narrowly escaped an attempt to assassinate murder him.
Among the heathens at Calama there was a certain Nectarius, who was a correspondent with Augustine.
Possidius successfully disarmed some of his enemies by his charity.
After the destruction of the town of Calama by the Vandals, Possidius moved to Hippo.
In the terrible months that preceded and followed that death, Possidius worked briskly to ensure that the books and papers of Augustine would survive the attack on Hippo, and remain available for future ages.