The Leader of the Opposition in Ireland is a de facto term sometimes used to describe the politician who leads the largest party in the Parliamentary Opposition in the lower house of the Irish Parliament, Dáil Éireann. In the Dáil, the Leader of the Opposition sits on the right-hand side of the Ceann Comhairle and directly opposite the Taoiseach. The role is not an official one and is not recognised in the Irish constitution, nor in legislation.

Dáil Éireann is the lower house, and principal chamber, of the Oireachtas, which also includes the president of Ireland and a senate called Seanad Éireann. It consists of 160 members, each known as a Teachta Dála. TDs represent 39 constituencies and are directly elected for terms not exceeding five years, on the system of proportional representation by means of the single transferable vote (PR-STV). Its powers are similar to those of lower houses under many other bicameral parliamentary systems and it is by far the dominant branch of the Oireachtas. Subject to the limits imposed by the Constitution of Ireland, it has power to pass any law it wishes, and to nominate and remove the Taoiseach. Since 1922, it has met in Leinster House in Dublin.