First Minister and deputy First Minister of Northern Ireland in the context of "Consociationalism"

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 allied, 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.

The Ulster Unionist Party (UUP) is a unionist political party in Northern Ireland. The UUP is the third oldest political party in the United Kingdom, and the oldest political party on the island of Ireland. The party was founded as the Ulster Unionist Council in 1905, emerging from the Irish Unionist Alliance in Ulster. Under Sir Edward Carson, it led unionist opposition to the Irish Home Rule movement. Following the partition of Ireland, it was the governing party of Northern Ireland between 1921 and 1972. It was supported by most unionist voters throughout the conflict known as the Troubles, during which time it was often referred to as the Official Unionist Party (OUP).

Under David Trimble, the party helped negotiate the Good Friday Agreement of 1998, which ended the conflict. Trimble served as the first First Minister of Northern Ireland from 1998 to 2002. However, it was overtaken as the largest unionist party in 2003 by the Democratic Unionist Party (DUP). As of 2022 it is the fourth-largest party in the Northern Ireland Assembly, after Sinn Féin, the DUP, and the Alliance Party. Since August 2024 the party has been led by Mike Nesbitt.