The Catholic Emancipation Act or The Roman Catholic Relief Act as it was better known, was passed by the Parliament of the United Kingdom on 24 March 1829, and received Royal Assent on 13 April. It was the culmination of the process of Catholic Emancipation throughout the nation.

In Ireland it repealed the Test Act 1673 and the remaining Penal Laws which had been in force since the passing of the Disenfranchising Act of the Irish Parliament of 1728. Its passage followed a vigorous campaign on the issue by Irish lawyer, Daniel O'Connell. O'Connell had firm support from the Prime Minister, the Duke of Wellington, as well as from the Whigs and liberal Tories.

In the 18th century attempts were made to obtain full political and civil liberties to British and Irish Roman Catholics. In Ireland, where the majority of the population were Catholics, the Relief Act of 1793 gave them the right to vote in elections, but not to sit in Parliament. In England the leading campaigners for Catholic emancipation were the Radical members of the House of Commons, Sir Francis Burdett and Joseph Hume.

By the beginning of the 19th century, William Pitt, the leader of Tories, became converted to the idea of Catholic emancipation. Pitt and his Irish Secretary, Lord Castlereagh, promised the Irish Parliament that Catholics would have equality with Protestants when it agreed to the Act of Union in 1801. When King George III refused to accept the idea of religious equality, Pitt and Castlereagh resigned from office.

In 1823 Daniel O'Connell founded the Catholic Association to campaign for the removal of discrimination against Catholics. In 1828 he was elected as M.P. for County Clare but as a Catholic he was not allowed to take his seat in the House of Commons. To avoid the risk of an uprising in Ireland, the British Parliament passed the Roman Catholic Relief Act in 1829, which granted Catholic emancipation and enabled O'Connell to take his seat.

The Act permitted members of the Catholic Church to sit in the parliament at Westminster. O'Connell had won a seat in a by-election for Clare in 1828 against the newly appointed President of the Board of Trade, Vesey Fitzgerald, an Anglican. Under the then extant penal law, O'Connell as a Roman Catholic, was forbidden to take his seat in Westminster. Sir Robert Peel, the Home Secretary, who had for all of his career opposed emancipation (and had, in 1815, challenged O'Connell to a duel) concluded: "though emancipation was a great danger, civil strife was a greater danger." Fearing a revolution in Ireland, Peel drew up the Catholic Relief Bill and guided it through the House of Commons. To overcome the vehement opposition of both the House of Lords and George IV, the Duke of Wellington worked tirelessly to ensure passage in the House of Lords, and threatened to resign as Prime Minister if the King did not give Royal Assent.

The Act was a compromise, as it effectively disenfranchised the minor landholders of Ireland, the so-called Forty Shilling Freeholders. The Act raised fivefold the economic qualifications for voting. Starting in the initial relief granting the vote by the Irish Parliament in 1793, any man renting or owning land worth at least forty shillings (the equivalent of two Pounds Sterling), had been permitted to vote. Under the Act, this was raised to ten pounds..

England before 1828 was a nation in which the vast majority of the people believed in the divine right of kings, and the legitimacy of a hereditary nobility, and in the rights and privileges of the Anglican Church. This system remained virtually intact until it suddenly collapsed in 1828, because Catholic emancipation undermines its central symbolic prop, the Anglican supremacy.

It has been said that: "The shattering of a whole social order....What was lost at that point... was not merely a constitutional arrangement, but the intellectual ascendancy of a world view, the cultural hegemony of the old elite." The political importance of emancipation was that it split the anti-reformers beyond repair and diminished their ability to block future reform laws, especially the great Reform Act of 1832.

Paradoxically, Wellington's success in forcing through emancipation converted many Ultra-Tories to demand reform of Parliament. They saw that the votes of the rotten boroughs had given the government its majority. Therefore it was an ultra-Tory, the Marquis of Blandford, who in February 1830 introduced the first major reform bill, calling for the transfer of rotten borough seats to the counties and large towns, the disfranchisement of non-resident voters, preventing Crown office-holders from sitting in Parliament, the payment of a salary to MPs, and the general franchise for men who owned property. The ultras believed that a widely based electorate could be relied upon to rally around anti-Catholicism.