Saint Patrick's Day became an official Christian feast day in which century?

Saint Patrick’s Day became an official Christian feast day in the 17th century.

The feast had been associated with Patrick for centuries, but it was formally placed on the Catholic Church’s liturgical calendar in the early 1600s. Waterford-born Franciscan scholar Luke Wadding played an important role in this development while working on the reform of the Roman Breviary.

The date is 17 March, traditionally regarded as Saint Patrick’s death date. In Ireland, the feast became a holy day of obligation for Catholics. It is also observed by the Church of Ireland and by several other Christian traditions, including Anglican, Lutheran and Eastern Orthodox communities.

The religious feast predates the modern parade-centred celebration. Public festivities, green clothing, shamrocks and large diaspora celebrations grew especially strongly in later centuries, with North American Irish communities helping shape the holiday’s modern international image.