The Catholic Church in the United Kingdom is part of the worldwide Catholic Church in communion with the Pope. While there is no ecclesiastical jurisdiction corresponding to the political union, this article refers to the Catholic Church's geographical representation in mainland Britain as well as Northern Ireland, ever since the establishment of the UK's predecessor Kingdom of Great Britain by the Union of the Crowns in 1707.

Catholic emancipation or Catholic relief was a process in the kingdoms of Great Britain and Ireland, and later the combined United Kingdom in the late 18th century and early 19th century, that involved reducing and removing many of the restrictions on Roman Catholics introduced by the Act of Uniformity, the Test Acts and the penal laws. Requirements to abjure (renounce) the temporal and spiritual authority of the pope and transubstantiation placed major burdens on Roman Catholics.