Unionism in Ireland is a political tradition that professes loyalty to the crown of the United Kingdom and to the union it represents with England, Scotland and Wales. The overwhelming sentiment of Ireland's Protestant minority, unionism mobilised in the decades following Catholic Emancipation in 1829 to oppose restoration of a separate Irish parliament. Since Partition in 1921, as Ulster unionism its goal has been to retain Northern Ireland as a devolved region within the United Kingdom and to resist the prospect of an all-Ireland republic. Within the framework of the 1998 Belfast Agreement, which concluded three decades of political violence, unionists have shared office with Irish nationalists in a reformed Northern Ireland Assembly. As of February 2024, they no longer do so as the larger faction: they serve in an executive with an Irish republican (Sinn Féin) First Minister.
Unionism became an overarching partisan affiliation in Ireland late in the nineteenth century. Typically Presbyterian agrarian-reform Liberals coalesced with traditionally Anglican Orange Order Conservatives against the Irish Home Rule Bills of 1886 and 1893. Joined by loyalist labour, on the eve of World War I this broad opposition to Irish self-government concentrated in Belfast and its hinterlands as Ulster unionism and prepared an armed resistance—the Ulster Volunteers.
Within the partition settlement of 1921 by which the rest of Ireland attained separate statehood, Ulster unionists accepted a home-rule dispensation for the six north-east counties remaining in the United Kingdom. For the next 50 years, the Ulster Unionist Party exercised the devolved powers of the Northern Ireland Parliament with little domestic opposition and outside of the governing party-political system at Westminster.
In 1972, the British government suspended this arrangement. Against a background of growing political violence, and citing the need to consider how Catholics in Northern Ireland could be integrated into its civic and political life, it prorogued the parliament in Belfast.
Over the ensuing three decades of The Troubles, unionists divided in their responses to power-sharing proposals presented, in consultation with the Republic of Ireland, by successive British governments. Following the 1998 Belfast Agreement, under which both republican and loyalist paramilitaries committed to permanent ceasefires, unionists accepted principles of joint office and parallel consent in a new Northern Ireland legislature and executive.
Renegotiated in 2006, relations within this consociational arrangement remained fraught. Unionists, with diminishing electoral strength, charged their nationalist partners in government with pursuing an anti-British cultural agenda and, post-Brexit, with supporting a trade regime, the Northern Ireland Protocol, that advances an all-Ireland agenda. In February 2024, two years after their withdrawal collapsed the devolved institutions, on the basis of new British government assurances they returned to the Assembly to form the first Northern Ireland government in which unionists are a minority.