Act of Union

Following the failed Irish Rebellion of 1798, the British government under Prime Minister William Pitt the Younger moved to bind Ireland more tightly to Great Britain. The Act of Union, which received royal assent in 1800 and took effect on January 1, 1801, merged the Kingdom of Great Britain and the Kingdom of Ireland into the United Kingdom of Great Britain and Ireland. Securing its passage required considerable patronage and persuasion within the Dublin legislature.

Under the Union, the separate Irish Parliament at Dublin was abolished, and Ireland was instead granted representation at Westminster, sending members to the House of Commons and peers to the House of Lords. Pitt had hoped to accompany the Union with Catholic Emancipation, allowing Catholics to sit in Parliament, but King George III opposed the measure as a violation of his coronation oath, and the reform was abandoned.

The Act of Union shaped Irish politics for over a century. The denial of Catholic Emancipation left lasting grievances, and the dissolution of the Dublin Parliament fueled later movements for repeal and Home Rule led by figures such as Daniel O'Connell. The arrangement endured until the early twentieth century, when the partition of Ireland and the creation of the Irish Free State undid much of what the Union had established.