The Pro-Cathedral owes its origins to the Penal Laws[b] which restricted Catholicism (and other non-Church of Ireland faiths) until the early nineteenth century.

For centuries, Roman Catholics could not celebrate Mass or the sacraments in public and were subject to severe penalties (hence the word penal).

By the early nineteenth century, many of the Penal Laws had either been repealed or were no longer enforced; an unsuccessful attempt had already been made to grant Catholic Emancipation.

[5] Though not a full cathedral, the new building became a symbol of the Irish nationalist spirit in the era following the ending of the Penal Laws.

In 1841, as the first Catholic Lord Mayor of Dublin in centuries, O'Connell formally celebrated his election by travelling in state to "the Pro" for High Mass.

[citation needed] St Mary's baptism register contains quite a few entries for children born in the nearby Rotunda hospital; they were probably baptised quite quickly due to the feared infant mortality rates of the 19th century.

W. T. Cosgrave, President of the Executive Council of the Irish Free State (prime minister) from 1922 to 1932 and a deeply religious Catholic, suggested that the burnt-out shell of the General Post Office, the location of the 1916 Rising, be turned into a cathedral, but the idea was not acted on, and the GPO was restored for use as a post office.

[citation needed] The Pro-Cathedral remains a focal point of religious and state ceremonial activity.

[citation needed] The major faiths held religious ceremonies in their main cathedral or pro-cathedral to mark the beginning of the law term or a session of parliament, which would be attended by the President of Ireland, the Taoiseach, ministers, the opposition, parliamentarians and members of the Diplomatic Corps.

State funerals of major figures including Michael Collins and former presidents Seán T. O'Kelly, Éamon de Valera, Patrick Hillery and Lord Mayor of Dublin Kathleen Clarke took place there.

For most of its existence, it possessed a massive Victorian altar and reredos by Peter Turnerelli, a Belfast-born sculptor of Italian parentage.

[citation needed] A large contingent of Italian artisans were employed by the church, to decorate the interior of the cathedral.

Walker's major rebuild of 1971 under the administrator Monsignor John Moloney and the most recent refurbishment of the instrument, by the same firm which was completed in the autumn of 1995.

It had its origins in a boys' choir formed in the 1890s by Vincent O'Brien, then a music teacher at St Mary's Place Christian Brothers School in Dublin.

It was at a performance of Palestrina's Missa Papae Marcelli at St. Teresa's Carmelite Church in Clarendon Street in 1898 that this choir came to the attention of Edward Martyn, their founding sponsor.

[10] The choir has travelled widely, singing at several cathedrals and venues throughout Ireland, Europe, and North America.