This county constituency comprised the central part of County Armagh. To the north was North Armagh, to the west were South Tyrone and North Monaghan, to the south were South Monaghan and South Armagh and to the east was West Down.
The constituency was a predominantly Conservative then Unionist area, although not as strongly so as some other parts of Northern Ireland. There were few contested elections and no instance of the same two parties contending against each other more than once.
In 1918 the Unionists defeated Sinn Féin by a solid margin. This was the first contested election for the seat since a 1900 by-election.
Sinn Féin contested the general election of 1918 on the platform that instead of taking up any seats they won in the United Kingdom Parliament, they would establish a revolutionary assembly in Dublin. In republican theory every MP elected in Ireland was a potential Deputy to this assembly. In practice only the Sinn Féin members accepted the offer.
The revolutionary First Dáil assembled on 21 January 1919 and last met on 10 May 1921. The First Dáil, according to a resolution passed on 10 May 1921, was formally dissolved on the assembling of the Second Dáil. This took place on 16 August 1921.