The Acts of Union 1800 are passed which merge the Kingdom of Great Britain and the Kingdom of Ireland into the United Kingdom of Great Britain and Ireland.

The Acts of Union 1800 (sometimes incorrectly referred to as a single 'Act of Union 1801') were parallel acts of the Parliament of Great Britain and the Parliament of Ireland which united the Kingdom of Great Britain and the Kingdom of Ireland (previously in personal union) to create the United Kingdom of Great Britain and Ireland. The acts came into force on 1 January 1801, and the merged Parliament of the United Kingdom had its first meeting on 22 January 1801.

Both acts remain in force, with amendments and some Articles repealed, in the United Kingdom, but have been repealed in its entirety in Ireland.