The Irish Rugby Football Union (IRFU), the body managing rugby union in the island of Ireland, both Republic of Ireland and Northern Ireland, is founded in Dublin on February 5, 1879. The IRFU has its head office at 10/12 Lansdowne Road and home ground at Aviva Stadium, where adult men’s Irish rugby union international matches are played. In addition, the Union also owns Kingspan Stadium in Belfast, Thomond Park in Limerick and a number of grounds in provincial areas that have been rented to clubs.

Initially, there are two unions, both founded in 1874. The Irish Football Union has jurisdiction over clubs in Leinster, Munster, and parts of Ulster. The Northern Football Union of Ireland controls the Belfast area. The IRFU is formed in 1879 as an amalgamation of these two organisations and branches of the new IRFU are formed in Leinster, Munster, and Ulster. The Connacht Branch is formed in 1900.

The IRFU is a founding member of the International Rugby Football Board, now known as World Rugby, in 1886 with Scotland and Wales. England refuses to join until 1890.

Following the political partition of Ireland into separate national states, Ireland, originally the Irish Free State then Éire, and Northern Ireland, a political division of the United Kingdom, the then Committee of the Irish Rugby Football Union decides that it will continue to administer its affairs on the basis of the full 32 Irish counties and the traditional four provinces of Ireland – Leinster (12 counties), Ulster (9 counties), Munster (6 counties), and Connacht (5 counties).

This leads to the unusual, but not unique, situation among international rugby union teams, where the Irish representative teams are drawn from players from two separate political, national territories. To maintain the unity of Irish rugby union and the linkages between North and South, the IRFU purchase a new ground in 1923 in the Ravenhill district of Belfast at a cost of £2,300. The last full International at Ravenhill involving Ireland for more than a half-century takes place in 1953–54 against Scotland who are victorious by 2 tries (6 points) to nil. Australia plays Romania in the 1999 World Cup at the ground. The next full International played at Ravenhill is the Rugby World Cup warm-up match against Italy in August 2007 due to the temporary closure of Lansdowne Road for reconstruction.

The four provincial branches of the IRFU first run cup competitions during the 1880s. Although these tournaments still take place every year, their significance has been diminished by the advent of an All-Ireland League of 48 Senior Clubs in 1990.

The four provincial teams have played an Interprovincial Championship since the 1920s and continue to be the focal point for players aspiring to the international level. These are Munster, Leinster, Ulster, and Connacht . All four provinces play at the senior level as members of the Guinness Pro12.

There are currently approximately 95,000 rugby players in total in Ireland. There are 56 clubs affiliated to the Ulster Branch, 71 to the Leinster Branch, 59 to the Munster Branch, and 19 to the Connacht Branch. In addition, there are 246 schools playing rugby: Ulster (107), Leinster (75), Munster (41) and Connacht (23).

The IRFU also has an Exiles Branch tasked with developing “Ireland-qualified” players (i.e., eligible to play internationally for Ireland through ancestry) living in England, Scotland, and Wales. Volunteers provide coaching, administration and development under the supervision of a paid development manager.