The legislative union of Kingdom of Great Britain and Kingdom of Ireland is completed, and the United Kingdom of Great Britain and Ireland is proclaimed.

Great Britain, also known as the Kingdom of Great Britain, was a sovereign state in Western Europe from 1707 to the end of 1800. The state was created by the 1706 Treaty of Union and ratified by the Acts of Union 1707, which united the Kingdom of England and the Kingdom of Scotland to form a single kingdom encompassing the whole island of Great Britain and its outlying islands, with the exception of the Isle of Man and the Channel Islands. The unitary state was governed by a single parliament at the Palace of Westminster, but distinct legal systems—English law and Scots law—remained in use, as did distinct educational systems and religious institutions, namely the Church of England and the Church of Scotland remaining as the national churches of England and Scotland respectively.

The Kingdom of Ireland was a dependent territory of England and then of Great Britain from 1542 to the end of 1800. It was ruled by the monarchs of England and then of Great Britain, and was administered from Dublin Castle by a viceroy appointed by the English king: the lord deputy of Ireland. Aside from brief periods, the state was dominated by the Protestant English minority, known as the Protestant Ascendancy. The Protestant Church of Ireland was the state church. The Parliament of Ireland was composed of Anglo-Irish nobles. From 1661, the administration controlled an Irish army. Although de jure styled as a kingdom, for most of its history it was de facto an English dependency. This status was enshrined in the Declaratory Act 1719, also known as the Irish Parliament Act 1719.

The United Kingdom of Great Britain and Ireland was the union of the Kingdom of Great Britain and the Kingdom of Ireland into one sovereign state, established by the Acts of Union in 1801. It continued in this form until 1927, when it evolved into the United Kingdom of Great Britain and Northern Ireland, after the Irish Free State gained a degree of independence in 1922.