On January 1, 1801, the Acts of Union 1800 goes into effect uniting Great Britain and Ireland to create the United Kingdom of Great Britain and Ireland. The Acts of Union 1800 consists of two acts with the same long title, An Act for the Union of Great Britain and Ireland. Both are passed in 1800.
Before these Acts, Ireland had been in personal union with England since 1541, when the Irish Parliament had passed the Crown of Ireland Act 1542 proclaiming King Henry VIII of England to be King of Ireland. Both Ireland and England had come in personal union with Scotland with the Union of the Crowns in 1603.
In 1707, the Kingdom of England and the Kingdom of Scotland were united into a single kingdom named the Kingdom of Great Britain. The Irish parliament at that time was subject to a number of restrictions that placed it subservient to the Parliament of England and, following the union of England and Scotland, the Parliament of Great Britain.
In the century that followed the union of England and Scotland, Ireland gained effective legislative independence from Great Britain through the Constitution of 1782. However, access to institutional power in Ireland was restricted to a small minority, the so-called Anglo-Irish of the Protestant Ascendancy. Frustration at the lack of reform eventually led to a rebellion in 1798, involving a French invasion of Ireland and seeking complete independence from Great Britain. The rebellion was crushed with much bloodshed and the subsequent drive for union between Great Britain and Ireland that passed in 1800 was motivated at least in part by the belief that the rebellion was caused as much by loyalist brutality as by the United Irishmen.
Each Act had to be passed in the Parliament of Great Britain and the Parliament of Ireland. The final passage of the Act in the Irish Parliament was achieved with substantial majorities, achieved in part according to contemporary documents through bribery, namely the awarding of peerages and honours to critics to get their votes.
Both Acts, though since amended, still remain in force in the United Kingdom but have been repealed in the Republic of Ireland.