The traditional feast day of the Kingship of Our Lord Jesus Christ is the last Sunday in October. A plenary indulgence may be gained on the feast day by the public recitation of the Act of Consecration of the Human Race to the Sacred Heart of Jesus. The usual conditions to acquire a plenary indulgence are: sacramental confession, worthy reception of Holy Communion, prayer for the intention of the Holy Father, and detachment from sin, even venial sins. If the conditions are not met, the indulgence will be partial.
Most Sweet Jesus, Redeemer of the human race, look down upon us, humbly prostrate before Thy altar. We are Thine and Thine we wish to be; but to be more surely united with Thee, behold each one of us freely consecrates himself today to Thy Most Sacred Heart. Many indeed have never known Thee; many, too, despising Thy precepts, have rejected Thee. Have mercy on them all, most merciful Jesus, and draw them to Thy Sacred Heart.
Be Thou King, O Lord, not only of the faithful who have never forsaken Thee; but also of the prodigal children who have abandoned Thee: grant that they may quickly return to their Father’s house, lest they die of wretchedness and hunger.
Be Thou King of those who are deceived by erroneous opinions, or whom discord keeps aloof, and call them back to the harbor of truth and unity of faith, so that soon there may be but one flock and one Shepherd.
Be Thou King also of all those who sit in the ancient superstition of the Gentiles, and refuse not Thou to deliver them out of darkness into the light and kingdom of God Grant, O Lord, to Thy Church assurance of freedom and immunity from harm; give peace and order to all nations, and make the earth resound from pole to pole with one cry: Praise to the Divine Heart that wrought our salvation; to It be glory and honor forever. Amen.
From Quas Primas, the Encyclical of Pope Pius XI, December 11, 1925, which established the Feast of Christ the King:
The kingship and empire of Christ have been recognized in the pious custom, practiced by many families, of dedicating themselves to the Sacred Heart of Jesus; not only families have performed this act of dedication, but nations, too, and kingdoms. In fact, the whole of the human race was at the instance of Pope Leo XIII, in the Holy Year 1900, consecrated to the Divine Heart. We institute the Feast of the Kingship of Our Lord Jesus Christ to be observed yearly throughout the whole world on the last Sunday of the month of October; the Sunday, that is, which immediately precedes the Feast of All Saints. We further ordain that the dedication of mankind to the Sacred Heart of Jesus, which our predecessor of saintly memory, Pope Pius X, commanded to be renewed yearly, be made annually on that day.