Saint Patrick (Latin: Patricius; Irish: Pádraig [ˈpˠɑːɾˠɪɟ] or [ˈpˠaːd̪ˠɾˠəɟ]; Welsh: Padrig) was a fifth-century Romano-British Christian missionary and bishop in Ireland. Known as the "Apostle of Ireland", he is the primary patron saint of Ireland, the other patron saints being Brigid of Kildare and Columba. Patrick was never formally canonised, having lived before the current laws of the Catholic Church in these matters. Nevertheless, he is venerated as a saint in the Catholic Church, the Lutheran Church, the Church of Ireland (part of the Anglican Communion), and in the Eastern Orthodox Church, where he is regarded as equal-to-the-apostles and Enlightener of Ireland.

The dates of Patrick's life cannot be fixed with certainty, but there is general agreement that he was active as a missionary in Ireland during the fifth century. A recent biography on Patrick shows a late fourth-century date for the saint is not impossible. According to tradition dating from the early Middle Ages, Patrick was the first bishop of Armagh and Primate of Ireland, and is credited with bringing Christianity to Ireland, converting a pagan society. He has been generally so regarded ever since, despite evidence of some earlier Christian presence.

According to Patrick's autobiographical Confessio, when he was about sixteen, he was captured by Irish pirates from his home in Britain and taken as a slave to Ireland. He writes that he lived there for six years as an animal herder before escaping and returning to his family. After becoming a cleric, he returned to spread Christianity in northern and western Ireland. In later life, he served as a bishop, but little is known about where he worked. By the seventh century, he had already come to be revered as the patron saint of Ireland.

His feast day is observed on 17 March, the supposed date of his death. It is celebrated in Ireland and among the Irish diaspora as a religious and cultural holiday. In the dioceses of Ireland, it is both a solemnity and a holy day of obligation.