The Protestant Ascendancy, also known simply as the Ascendancy, was the political, economic, and social domination of Ireland between the 17th century and the early 20th century by a minority of landowners, Protestant clergy, and members of the professions, all members of the Established Church (Anglican; Church of Ireland or the Church of England). The Ascendancy excluded other groups from politics and the elite, most numerous among them Roman Catholics but also members of the Presbyterian and other Protestant denominations, along with non-Christians such as Jews, until the Reform Acts (1832–1928).

The gradual dispossession of large holdings belonging to several hundred native Catholic nobility and other landowners in Ireland took place in various stages from the reigns of the Catholic Mary I (1553–1558) and her Protestant half-sister Elizabeth I (1558–1603) onwards. Unsuccessful revolts against English rule in 1595–1603 and 1641–53 and then the 1689–91 Williamite Wars resulted in much Irish land confiscated by the Crown, and then sold to people who were thought loyal, most of whom were English and Protestant. English soldiers and traders became the new ruling class, as its richer members were elevated to the Irish House of Lords and eventually controlled the Irish House of Commons (see Plantations of Ireland). This class became collectively known as the Anglo-Irish.

From the 1790s the phrase became used by the main two identities in Ireland: nationalists, who were mostly Catholics, used the phrase as a "focus of resentment", while for unionists, who were mostly Protestants, it gave a "compensating image of lost greatness".