The Constitution of 1782 is a collective term given to a series of legal changes which freed the Parliament of Ireland, a mediaeval body made up of the Irish House of Commons and the Irish House of Lords, of legal restrictions that had been imposed since mediaeval times by successive English and British government on its work. These restrictions had in effect allowed the Irish executive of the British Lord Lieutenant of Ireland to control the parliamentary agenda and to restrict its ability to legislate for the interests of Ireland rather than the kingdoms of England (pre-1707) and Great Britain (1707-1800).

The most notorious restriction had been Poyning's Law of 1492.

These restrictions were all lifted in 1782, producing a period of unheard-of legislative freedom. This period came to be known as Grattan's Parliament after Henry Grattan, a major campaigner for reform in the Parliament's Irish House of Commons.

The Irish Parliament merged with the Parliament of Great Britain in 1801, ending the period of legislative freedom. From 1801 to 1922, Ireland legally was part of the United Kingdom of Great Britain and Ireland and legislated for from the United Kingdom parliament in Westminster.

The eighteenth century Old Irish Parliament House in College Green in Dublin (which was the first purpose-built two-chamber parliament in the world, pre-dating the nineteenth century Palace of Westminster and the United States Capitol), survives today under the name of the Bank of Ireland, College Green. While its famed Irish House of Commons chamber was dismantled after the Act of Union 1800, the magnificent Irish House of Lords chamber still exists and is worth a visit by anyone visiting Dublin. Visits are free. It is open during normal Bank opening hours.