Saint Prosper was born in Aquitaine around the year 390. He was a renowned lay theologian, although few details of his life are known.
We know Saint Prosper chiefly from his writings. A contemporary writer described him as "a holy and venerable man." Like Saint Augustine, Saint Prosper was also an opponent of the Pelagian heresy. This wise man seems to have spent his life embroiled in controversies with heretics. Many of Saint Prosper's writings echo the teaching of Saint Augustine (June 15) on grace and free will. Though he never met Augustine, he was an aggressive propagandist for the Augustinian doctrine of grace. After Augustine's death he wrote three series of Augustinian defenses, especially against Saint Vincent of Lerins and Saint John Cassian (it should be noted that the Orthodox position aligns more with the latter rather than Augustine). In speaking of Pelagianism in Rome, Saint Photios the Great says the following: "Not long afterwards, when the shameless heresy again sprang up from an evil root, certain persons at Rome openly expressed themselves in favor of it. But Prosper, truly a man of God, in his pamphlets against them, soon crushed them, while Leo still occupied the papal throne."
In Saint Prosper, science was joined to virtue. It is evident that he applied himself to literature, and especially to acquiring knowledge of Holy Scripture. He was no less an expert in human sciences than he was in theology. He excelled particularly in mathematics, astronomy, and chronology. His great learning and holiness made him well known throughout the entire Church.
Saint Prosper has sometimes been identified, mistakenly, with Saint Paulinus of Reggio (June 25), who was a bishop. Everything we know about him leads us to believe that Saint Prosper was not a bishop, nor even a priest. In a poem to his wife he wrote: "Lift me up again if I fall; correct yourself if I point out some fault. Let it never be sufficient for us to be one body, let us also be one soul." By 428, Saint Prosper persuaded his wife to become a nun, and he entered a monastery at Marseilles. When Saint Leo the Great was chosen as the Bishop of Rome in 440, he sent for Prosper to become his secretary. Many historians believe that the admirable treatise "On the Incarnation of the Word," which is ascribed to Saint Leo, is actually the work of Saint Prosper. It is possible, however, that Saint Leo may have reworked it in his own style.
Saint Prosper reposed in Rome, sometime after 455.
The icon of Saint Prosper depicts him holding a scroll which reads: "The Orthodox faith subdues the monster of heresy."
Apolytikion in the First Tone
Come, you faithful, let us venerate Prosper, this new Father of the Church, the child of Aquitaine and glory of the Gauls, an imitator of the Holy Apostles; from all sorts of threats against Orthodoxy he delivers those who cry to him with faith: Glory to Him Who has given you this knowledge, glory to Him Who has enlightened you, glory to Him Who saves us by your prayers.