In 1903, St Patrick's Day became an official public holiday in Ireland. This was thanks to the Bank Holiday (Ireland) Act 1903, an act of the United Kingdom Parliament introduced by Irish Member of Parliament James O'Mara. O'Mara later introduced the law which required that public houses be shut on 17 March after drinking got out of hand, a provision that was repealed in the 1970s.
The first St Patrick's Day parade in Ireland was held in Waterford in 1903. The week of St Patrick's Day 1903 had been declared Irish Language Week by the Gaelic League and in Waterford, they opted to have a procession on Sunday 15 March. The procession comprised the Mayor and members of Waterford Corporation, the Trades Hall, the various trade unions and bands who included the 'Barrack St Band' and the 'Thomas Francis Meagher Band'. The parade began at the premises of the Gaelic League in George's St and finished in the Peoples Park, where the public was addressed by the Mayor and other dignitaries. On Tuesday 17 March, most Waterford businesses—including public houses—were closed and marching bands paraded as they had two days previously. The Waterford Trades Hall had been emphatic that the National Holiday be observed.
On St Patrick's Day 1916, the Irish Volunteers—an Irish nationalist paramilitary organization—held parades throughout Ireland. The authorities recorded 38 St Patrick's Day parades, involving 6,000 marchers, almost half of whom were said to be armed. The following month, the Irish Volunteers launched the Easter Rising against British rule. This marked the beginning of the Irish revolutionary period and led to the Irish War of Independence and the Civil War. During this time, St Patrick's Day celebrations in Ireland were muted, although the day was sometimes chosen to hold large political rallies. The celebrations remained low-key after the creation of the Irish Free State; the only state-organized observance was a military procession and trooping of the colors, and an Irish-language mass attended by government ministers.
The church calendar avoids the observance of saints' feasts during certain solemnities, moving the saint's day to a time outside those periods. St Patrick's Day is occasionally affected by this requirement, when 17 March falls during Holy Week. This happened in 1940 when Saint Patrick's Day was observed on 3 April to avoid it coinciding with Palm Sunday, and again in 2008, where it was officially observed on 15 March. St Patrick's Day will not fall within Holy Week again until 2160. However, the popular festivities may still be held on 17 March or on a weekend near to the feast day.
The first St Patrick's Festival was held on 17 March 1996. In 1997, it became a three-day event, and by 2000 it was a four-day event. By 2006, the festival was five days long; more than 675,000 people attended the 2009 parade. Overall 2009's five-day festival saw almost 1 million visitors, who took part in festivities that included concerts, outdoor theatre performances, and fireworks. The Skyfest which ran from 2006 to 2012 formed the centerpiece of the St Patrick's festival.
On two occasions, parades across the Republic of Ireland have been canceled from taking place on St Patrick´s Day, with both years involving health and safety reasons. In 2001, as a precaution to the foot-and-mouth outbreak, St Patrick´s Day celebrations were postponed to May