St Patrick’s Day was first celebrated as a Christian feast day for St Patrick in Ireland around the 9th–10th century, though the Church formally established March 17 as his feast day in 1631.

Quick Scoop: Origins of St Patrick’s Day

Early religious celebrations (Ireland)

  • Historians believe the earliest St Patrick’s Day celebrations date to about the 9th or 10th century in Ireland, focused on a special religious feast rather than parades.
  • These early observances marked a break from Lenten fasting, with people gathering for Mass and a communal meal in honor of the saint.

Official feast day in the Church

  • The Catholic Church formally placed St Patrick’s feast on 17 March in 1631, creating the annual liturgical celebration that underpins the modern holiday.
  • This Church recognition turned a local devotional tradition into a fixed date in the religious calendar, which later helped it spread worldwide.

First parades and public festivities

  • The first known St Patrick’s Day parade took place not in Ireland but in St. Augustine, Florida, in 1601, organized by an Irish vicar in the Spanish colony.
  • New York’s famous parade tradition began later; Irish soldiers marched there on 17 March 1772 to honor St Patrick, helping shift the day toward public celebration and Irish pride.

Today’s global “green” holiday

  • Now, St Patrick’s Day on March 17 is widely marked with green clothing, parades, and festivals, but its roots lie in that much older religious feast for Ireland’s patron saint.
  • The modern, party-like version really took shape from the 18th century onward, especially among Irish communities abroad who used it to celebrate identity and heritage.

TL;DR:
It likely began as a religious feast in Ireland in the 9th–10th century, was officially set as a Church feast on March 17 in 1631, and only centuries later evolved into the parade-filled global celebration we know now.

Information gathered from public forums or data available on the internet and portrayed here.