Pelagius was a Christian theologian active in the late fourth and early fifth centuries CE, likely of British origin. A well-educated moral reformer in Rome, he taught that rigorous human effort and free will could achieve a sinless life, directly opposing Augustine of Hippo’s views on grace. After fleeing Rome in 410 CE, his doctrines were condemned as heretical at the Council of Carthage in 418 CE, leading to his excommunication.

Though authorship is often disputed, major works attributed to him include the fragmentary treatise On Free Will, his Confession of Faith to Pope Innocent, the exegetical Commentaries on the Thirteen Epistles of Paul, and the hortatory Letter to Demetrias. Many survive only in fragments preserved by his opponents.

Pelagius is the namesake of the Pelagian controversy. Augustine’s forceful refutation of his teachings on human nature and free will profoundly shaped subsequent Western Christian doctrine on grace, original sin, and predestination.