March 17, popularly known as St. Patrick’s Day, is believed to be his death date and is the date celebrated as his feast day. The day became a feast day in the universal church due to the influence of the Waterford-born Franciscan scholar Luke Wadding, as a member of the commission for the reform of the Breviary  in the early part of the 17th century.
For most of Christianity’s first thousand years, canonisations were done on the diocesan or regional level. Relatively soon after the death of people considered to be very holy people, the local Church affirmed that they could be liturgically celebrated as saints. As a result, St. Patrick has never been formally canonised by a Pope; nevertheless, various Christian churches declare that he is a Saint in Heaven (he is in the List of Saints). He is still widely venerated in Ireland and elsewhere today.
Saint Patrick was a Christian missionary and is the patron saint of Ireland along with Brigid of Kildare and Columba. Patrick was born in Roman Britain. When he was about sixteen he was captured by Irish raiders and taken as a slave to Ireland, where he lived for six years before escaping and returning to his family. He entered the church, as his father and grandfather had before him, becoming a deacon and a bishop. He later returned to Ireland as a missionary, working in the north and west of the island, but little is known about the places where he actually worked and no link can be made with Patrick and any church. By the eighth century he had become the patron saint of Ireland.