Irresistible grace (also called effectual grace, effectual calling, or efficacious grace) is a doctrine in Christian theology particularly associated with Calvinism, which teaches that the saving grace of God is effectually applied to those whom he has determined to save (the elect) and, in God's timing, overcomes their resistance to obeying the call of the gospel, bringing them to faith in Christ. It is to be distinguished from prevenient grace, particularly associated with Arminianism, which teaches that the offer of salvation through grace does not act irresistibly in a purely cause-effect, deterministic method, but rather in an influence-and-response fashion that can be both freely accepted and freely denied.

Some claim that fourth-century Church Father Augustine of Hippo taught that God grants those whom he chooses for salvation the gift of persevering grace, and that they could not conceivably fall away.^{[citation needed]} This doctrine gave rise to the doctrine of irresistible grace (gratia irresistibilis), though the term was not used during Augustine's lifetime.

According to Calvinism, those who obtain salvation do so, not by their own "free" will, but because of the sovereign grace of God. That is, men yield to grace, not finally because their consciences were more tender or their faith more tenacious than that of other men. Rather, the willingness and ability to do God's will are evidence of God's own faithfulness to save men from the power and the penalty of sin, and since man is dead in sin and a slave to it, he cannot decide or be wooed to follow after God: God must powerfully intervene by giving him life and irresistibly drawing the sinner to himself. In short, Calvinism argues that regeneration must precede faith. In contrast, Arminianism argues that God’s grace through Jesus Christ stirs up a willingness to know God and respond to the gospel before regeneration; it is how God intervenes that separates Calvinism from Arminianism.

Calvin says of this intervention that "it is not violent, so as to compel men by external force; but still it is a powerful impulse of the Holy Spirit, which makes men willing who formerly were unwilling and reluctant." Despite the denial by Calvin and within the Calvinist confessions John Gill says that "this act of drawing is an act of power, yet not of force; God in drawing of unwilling, makes willing in the day of His power: He enlightens the understanding, bends the will, gives an heart of flesh, sweetly allures by the power of His grace, and engages the soul to come to Christ, and give up itself to Him; he draws with the bands of love. Drawing, though it supposes power and influence, yet not always coaction and force: music draws the ear, love the heart, and pleasure the mind."

Christians associated with Arminianism, such as John Wesley and part of the Methodist movement, reject this Calvinist doctrine. They believe that as Adam and Eve were free to choose between right and wrong, humanity is able, as a result of the prevenient or preceding grace of God through Jesus Christ, to choose to turn from sin to righteousness and believe on Jesus Christ who draws all of humanity to himself. And I, if I be lifted up from the earth, will draw all men unto me.^{John 12:32} In this view, (1) after God's universal dispensation of grace to mankind, the will of man, which was formerly adverse to God and unable to obey, can now choose to obey through the work of Christ; and (2) although God's grace is a strong initial catalyst to effect salvation, it is not irresistible but may be ultimately resisted and rejected by a human being.

Both Calvinism and Arminianism agree that the question of the resistibility of grace is inexorably bound up with the theological system's view of the sovereignty of God. The fundamental question is whether God can allow individuals to accept or reject his grace and yet remain sovereign. If so, then grace can be resistible. If not, then grace must be irresistible.

This different understanding of sovereignty is often attributed^{[by whom?]} to an improper understanding of total depravity. However, both Calvin and Arminius taught total depravity. Total depravity is expressly affirmed in Article III of the Five articles of Remonstrance. Nevertheless, Calvinist Charles Hodge says, "The (Arminian) and (Roman Catholic) doctrine is true, if the other parts of their doctrinal system are true; and it is false if that system be erroneous. If the (Calvinistic) doctrine concerning the natural state of man since the fall, and the sovereignty of God in election, be Scriptural, then it is certain that sufficient grace does not become efficacious from the cooperation of the human will." Hodge's argument follows Calvinist teaching which denies that the work of Jesus Christ empowers humanity to respond to the gospel before regeneration.

Calvinism's rejection of prevenient grace leaves humanity in a state of Total Depravity which requires regeneration of an individual before that individual is capable to believe or repent. John the Baptist called all to his baptism for the remission of sins^{Mark 1:4} and multitudes responded without regeneration.^{Mark 1:5} The New Testament regularly calls individuals to repent and believe with no indication that they had been previously regenerated. The Apostle Peter called the Jews to repent and be converted.^{Acts 3:19} Jesus promised that the Holy Spirit would convict the world of sin.^{John 16:8} Calvinism's response is found in Limited Atonement. So as a result of the Calvinist understanding of God's sovereignty, one must conclude that God's election does not depend upon any human response, necessitating a belief in (1) both Total Depravity and Unconditional Election, (2) Irresistible Grace rather than Prevenient Grace, and (3) Limited Atonement; if any of these beliefs are rejected, this logic fails.