The Passage of the Act
The following months after Pitt's initial failure, events became favourable towards the government. The anti-unionists had nothing positive to offer so leading members of the Roman Catholic clergy supported the union, encouraged by the belief that Catholic emancipation would follow. Fears of French invasion resurfaced in 1799-1800 so this shook the anti-unionist resolve of some members of the Ascendancy. Pitt controlled patronage- there was no chance of an anti-unionist administration coming to power in Britain.
Ultimately, everything would turn on the vote in the Irish House of Commons (HoC) and the Chief Sec (Castlereagh) was determined to ensure the govt's win and thus employed influence, pressure and bribery to ensure that MP's voted in favour of union. Anti-unionists were forced to conform or lose their seats and one fifth of the total MP's entered the HoC between 1799 and 1800.
So, in 1800 when Irish parliament met again to reconsider the government's motion, it concented by a vote of 158 to 115. In the spring of both the HoC and HoL accepted the plans for the Act of Union and after a few minor amendments, so did the Westminster parliament. It was fully passed in August 1800.
It is argued that it was Castlereagh's use of corruption that lead to the Irish parliament agreeing to its own extinction. However, recent historians believe that there was nothing exceptional about Castlereagh's methods, only their scale. The anti-unionists won the first round of the government in 1799 because of their united resistance, they then failed because they had no agreed alternative once it became clear the govt wanted to continue with its plan.
The United Kingdon of Great Britain and Ireland was established on the 1st January 1801. The Irish parliament disappeared and Ireland was incorporated into the British…