The union took effect on 1 January 1801. There was no new election for the members of the 1st Parliament of the United Kingdom, as the House of Commons was composed of members elected to the previous Parliaments of Ireland and Great Britain. The constituencies consisted of the whole of County Armagh, excluding the part in the Parliamentary borough constituency of Armagh City.
Catholics were excluded from taking Irish seats in Parliament from 1691 until 1829. See Catholic emancipation for further details.
Catholics, who were otherwise qualified to vote, had to take various oaths before doing so; under Acts of 1691 and 1703. An Act of 1727 prohibited "papists" from voting at all. They were not again permitted to qualify to vote until 1793.
Before 1885 there was a restrictive property based franchise. In 1829 the traditional county 40 shilling freehold landowning qualification was changed to a £10 qualification (which was an increase to five times the previous level). It was not until the householder franchise was introduced for county elections, in the electoral reforms which took effect in 1885, that most (but not all) adult males became voters.
In these circumstances most Members of Parliament came from a limited number of Protestant aristocratic and gentry families. There were few contested elections.
In the first half century or so after the union this constituency was fairly evenly balanced between Whig/Liberal and Tory/Conservative parties. Thereafter the area became more Conservative.
The constituency was represented by two MPs from 1801 until 1885, and by one MP from 1922 until 1983. In 1885, it was split into Mid Armagh, North Armagh and South Armagh.
After 1832, when registration of voters was introduced, a turnout figure is given for contested elections. In two-member elections, when the exact number of participating voters is unknown, this is calculated by dividing the number of votes by two. To the extent that voters did not use both their votes this will be an underestimate of turnout. If the electorate figure is unknown the last known electorate figure is used to provide an estimate of turnout.
Where a party had more than one candidate in one or both of a pair of successive elections change is calculated for each individual candidate, otherwise change is based on the party vote.