The Last Judgment will come when Christ returns in glory. Only the Father knows the day and the hour; only he determines the moment of its coming. Then through his Son Jesus Christ he will pronounce the final word on all history. We shall know the ultimate meaning of the whole work of creation and of the entire economy of salvation and understand the marvellous ways by which his Providence led everything towards its final end. The Last Judgment will reveal that God's justice triumphs over all the injustices committed by his creatures and that God's love is stronger than death.
Source: Catechism of the Catholic Church (Vatican.va)