Watson's Biblical & Theological Dictionary 
a sect that arose in the fifth century. Pelagius was a British monk, of some rank, and very exalted reputation. He, with his friend Celestius, travelled to Rome, where they resided very early in the fifth century, and opposed with warmth certain received notions respecting original sin, and the necessity of divine grace. What reception their doctrines met with at Rome does not appear; but their virtue excited general approbation. On the approach of the Goths, they retired to Africa, where Celestius remained, with a view of gaining admittance as a presbyter into the church of Carthage. Pelagius proceeded to Palestine, where he enjoyed the favour and protection of John, bishop of Jerusalem. But his friend and his opinions met with a very different reception from St. Augustine, the celebrated bishop of Hippo. Whatever parts were visited by these unorthodox friends, they still asserted their peculiar opinions; and they were gradually engaged in a warm contest, in the course of which they were probably led to advance more than had originally occurred to them.
In contending for the truth of their doctrines, they are said to have asserted, "that mankind derived no injury from the sin of Adam; that we are now as capable of obedience to the will of God as he was; that, otherwise, it would have been cruel and absurd to propose to mankind the performance of certain duties, with the sanction of rewards, and the denunciation of punishments; and that, consequently, men are born without vice, as well as without virtue." Pelagius is charged also with having maintained, "that it is possible for men, provided they fully employ the powers and faculties with which they are endued, to live without sin;" and though he did not deny that external grace, or the doctrines and motives of the Gospel, are necessary, yet he is said to have rejected the necessity of internal grace, or the aids of the divine Spirit. He acknowledged, "that the power we possess of obeying the will of God, is a divine gift;" but asserted, "that the direction of this power depends upon ourselves; that natural death is not a consequence of the sin of Adam, but of the frame of man; and that Adam would have died, though he had not sinned." Isidore, Chrysostom, and Augustine strenuously opposed these opinions; and the latter procured their condemnation in a synod held at Carthage in 412.
They were, however, favourably received at Rome, and Pope Zozimus was at the head of the Pelagian party: but his decision against the African bishops, who had opposed Pelagianism, was disregarded by them, and the pontiff yielded at length to their reasonings and remonstrances, and condemned the men whom he had before honoured with his approbation. The council of Ephesus likewise condemned the opinions of Pelagius and Celestius; and the Emperor Honorius, in 418, published an edict, which ordained that the leaders of the sect should be expelled from Rome, and their followers exiled. Some of the Pelagians taught that Christ was a mere man, and that men might lead sinless lives, because Christ did so; that Jesus became Christ after his baptism, and God after his resurrection; the one arising from his unction, the other from the merit of his passion. The Pelagian controversy, which began with the doctrines of grace and original sin, was extended to predestination, and excited continual discord and division in the church. It must however be recollected, that we are acquainted with the sentiments of Pelagius only through the medium of his opponents; and that it is probable that they were much misrepresented. See Augustine .
The followers of the truly evangelical Arminius, or those who hold the tenet of general redemption with its concomitants, have often been greatly traduced, by the ignorant among their doctrinal opponents, as Pelagians, or at least as Semi-Pelagians. It may therefore serve the cause of truth to exhibit the appropriate reply which the Dutch Arminians gave to this charge when urged against them at the synod of Dort, and which they verified and maintained by arguments and authorities that were unanswerable. In their concluding observations they say, "From all these remarks a judgment may easily be formed at what an immense distance our sentiments stand from the dogmatical assertions of the Pelagians and Semi- Pelagians on the grace of God in the conversion of man. Pelagius, in the first instance, attributed all things to nature: but we acknowledge nothing but grace. When Pelagius was blamed for not acknowledging grace, he began indeed to speak of it, but it is evident that by grace he understood the power of nature as created by God, that is, the rational will: but by grace we understand a supernatural gift. Pelagius, when afterward pressed with passages of Scripture, also admitted this supernatural grace; but he placed it solely in the external teaching of the law: though we affirm that God offers his word to men, yet we likewise affirm that he inwardly causes the understanding to believe. Subsequently Pelagius joined to this external grace that by which sins are pardoned: we acknowledge not only the grace by which sins are forgiven, but also that by which men are assisted to refrain from the commission of sin. In addition to his previous concessions Pelagius granted, that the grace of Christ was requisite beside the two kinds which he had enumerated; but he attributed it entirely to the doctrine and example of Christ that we are aided in our endeavours not to commit sin: we likewise admit that the doctrine and example of Christ afford us some aid in refraining from sin, but in addition to their influence we also place the gift of the Holy Spirit with which God endues us, and which enlightens our understandings, and confers strength and power upon our will to abstain from sinning. When Pelagius afterward owned the assistance of divine power inwardly working in man by the Holy Spirit, he placed it solely in the enlightening of the understanding: but we believe, that it is not only necessary for us to know or understand what we ought to do, but that it is also requisite for us to implore the aid of the Holy Spirit that we may be rendered capable of performing, and may delight in the performance of, that which it is our duty to do. Pelagius admitted grace,—but it has been a question with some whether he meant only illumination, or, beside this, a power communicated to the will;—he admitted grace, but he did this only to show that by means of it man can with greater ease act aright: we, on the contrary, affirm that grace is bestowed, not that we may be able with greater ease to act aright, (which is as though we can do this even without grace,) but that grace is absolutely necessary to enable us to act at all aright. Pelagius asserted, that man, so far from requiring the aid of grace for the performance of good actions, is, through the powers implanted in him at the time of his creation, capable of fulfilling the whole law, of loving God, and of overcoming all temptations: we, on the contrary, assert that the grace of God is required for the performance of every act of piety. Pelagius declared, that by the works of nature man renders himself worthy of grace: but we, in common with the church universal, condemn this dogma. When Pelagius afterward himself condemned this tenet, he understood by grace, partly natural grace, which is antecedent to all merit, and partly remission of sins, which he acknowledged to be gratuitous; but he added, that through works performed by the powers of nature alone, at least through the desire of good and the imperfect longing after it, men merit that spiritual grace by which they are assisted in good works: but we declare, that men will that which is good on account of God's prevenience or going before them by his grace, and exciting within them a longing after good; otherwise grace would no longer be grace, because it would not be gratuitously bestowed, but only on account of the merit of man." That many who have held some tenets in common with the true Arminians have been, in different degrees, followers of Pelagius is well known; but the original Arminians were in truth as far from Pelagian or Semi-Pelagian errors, granting the opinions of Pelagius to be fairly reported by his adversaries, as the Calvinists themselves. This is also the case with the whole body of Wesleyan Methodists, and of the cognate societies to which they have given rise, both in Great Britain and America.
Charles Buck Theological Dictionary 
A sect who appeared about the end of the fourth century. They maintained the following doctrines:
1. That Adam was by nature mortal, and, whether he had sinned or not, would certainly have died.
2. That the consequences of Adam's sin were confined to his own person.
3. That new-born infants are in the same situation with Adam before the fall.
4. That the law qualified men for the kingdom of heaven, and was founded upon equal promises with the Gospel.
5. That the general resurrection of the dead does not follow in virtue of our Saviour's resurrection.
6. That the grace of God is given according to our merits.
7. That this grace is not granted for the performance of every moral act; the liberty of the will and information in points of duty being sufficient. The founder of this sect was Pelagius, a native of Great Britain. He was educated in the monastery of Banchor, in Wales, of which he became a monk, and afterwards an abbot. In the early part of his life he went over to France, and thence to Rome, where he and his friend Celestius propagated their opinions, though in a private manner. Upon the approach of the Goths, A. D. 410, they retired from Rome, and went first into Sicily, and afterwards into Africa, where they published their doctrines with more freedom. From Africa, Pelagius passed into Palestine, while Celestius remained at Carthage, with a view to preferment, desiring to be admitted among the presbyters of that city. But the discovery of his opinions having blasted all his hopes, and his errors being condemned in a council held at Carthage, A. D. 412, he departed from that city, and went into the East. It was from this time, that Augustin, the famous bishop of Hippo, began to attack the tenets of Pelagius and Celestius in his learned and elegant writings; and to him, indeed, is principally due the glory of having suppressed this sect in its very birth.
Things went more smoothly with Pelagius in the East, where he enjoyed the protection and favour of John, bishop of Jerusalem, whose attachment to the sentiments of Origen led him naturally to countenance those of Pelagius, on account of the conformity that there seemed to be between these two systems. Under the shadow of this powerful protection, Pelagius made a public profession of his opinions, and formed disciples in several places. And by Orosius, a Spanish presbyter, whom Augustin had sent into Palestine for that purpose, before an assembly of bishops met at Jerusalem, yet he was dismissed without the least censure; and not only so, but was soon after fully acquitted of all errors by the council of Diospolis. This controversy was brought to Rome, and referred by Celestius and Pelagius to the decision of Zosimus, who was raised to the pontificate, A. D. 417. The new pontiff, gained over by the ambiguous and seemingly orthodox confession of faith that Celestius, who was now at Rome, had artfully drawn up, and also by the letters and protestations of Pelagius, pronounced in favour of the faith, and unjustly persecuted by their adversaries.
The African bishops, with Augustin at their head, little affected with this declaration, continued obstinately to maintain the judgment they had pronounced in this matter, and to strengthen it by their exhortations, their letters and their writings, Zosimus yielded to the perseverance of the Africans, changed his mind, and condemned, with the utmost severity, Pelagius and Celestius, whom he had honoured his protection. This was followed by a train of evils, which pursued these two monks without interruption. They were condemned, says Mosheim, by that same Ephesian council which had launched its thunder at the head of Nestorius. In short, the Gauls, Britons, and Africans, by their councils, and emperors, by their edicts and penal laws, demolished this sect in its infancy, and suppressed it entirely before it had acquired any tolerable degree of vigour or consistence.