Augustine contributed to Christian thought with some pivotal works that have developed Christian doctrine. His works continue to be relevant today in theology and Christian practice. He responded to some of the main controversies the Catholic Church faced in the fourth and fifth centuries on the doctrine of Trinity, Christology, and Grace. He believed that only the grace of God can bridge the chasm that sin creates between the Creator and creatures. Only grace can usher believers into God’s salvation. He also claimed that those to whom God chooses to give grace, God does so despite their power to resist. Pelagius and his followers, on the other hand, arguably misinterpreted Augustine’s doctrine of grace especially on the aspect of original sin; so Pelagius therefore denied the efficacy of baptism. He also claimed that Augustine denied the existence of free will in humans and that he held that free will was destroyed by sin, and thus free will was incompatible with Augustine’s doctrine of grace. He also accused Augustine of being a Manichean because of his doctrine of concupiscence. On the contrary to Pelagius, Augustine advanced the view that humans lost their free will only when Adam sinned. He, therefore, emphasized the believer’s restoration in Christ and the need for the grace of Christ. Therefore, the point of this project is to examine Augustine’s doctrine of grace including its development and key tenets. The analysis includes Pelagius’ criticism and its effect on the development of Augustine’s arguments on free will and efficacy of grace. Before its conclusion, Augustine’s response to Pelagius and his proponents becomes key in the project.