The Act of Union of 1800 was a greater turning point in the history of Britain than either the French Revolution or the Reform Act of 1832. It ushered in the nineteenth century by incorporating Ireland into the United Kingdom and thereby put Irish problems at the top of the agenda of British politics, not least because the 100 members returned to Westminster from the province were determined to keep them there.

Sixty-four of these MPs sat for the thirty-two counties. As in England the franchise was the possession of a forty-shilling freehold. Since owners of such freeholds were relatively rare in Ireland, however, a much larger proportion of the county electorates consisted of leaseholders for lives, making electors more dependent upon landlords than English voters were. The most crucial difference, however, was the fact that nearly 80 per cent of the population of Ireland was Catholic. Although Catholics could not legally stand for parliament until 1829, they could vote in parliamentary elections. The rest of the electorate was divided between the established Church of Ireland and various other Protestant denominations of which the Presbyterians in Ulster were the largest.

Where mainland Britain was becoming increasingly industrialised in the early nineteenth century, Ireland's economy, paradoxically, was becoming more agrarian. Although urbanisation was occurring, especially with the growth of Belfast, nevertheless the country remained overwhelmingly rural, and the main industry, textiles, was in serious decline.