Mid Armagh was a constituency in the Parliament of the United Kingdom. It was created by the Redistribution of Seats Act and first used at the 1885 general election. It returned one Member of Parliament (MP) until it was abolished with effect from the 1922 general election.

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.

1885–1922: The baronies of Armagh and Tiranny, that part of the barony of Oneilland West not contained within the constituency of North Armagh, that part of the barony of Fews Lower contained within the parishes of Kildarton and Mullaghbrack, the parish of Lisnadill excluding the townlands of Ballymacnab, Cashel, Foley and Seagahan, and the townlands of Corhammock and Edenykennedy in the parish of Kilclooney, that part of the barony of Orior Lower consisting of that part of the parish of Kilmore not contained within the constituency of North Armagh and the townlands of Aughlish, Ballymore, Ballysheil Beg, Ballysheil More, Cargans, Clare, Cloghoge, Coolyhill, Derryallen, Drumnaleg, Druminure, Drumnaglontagh, Lisbane, Lisnakea, Mavemacullen, Monclone, Moodoge, Mullantur, Mullaghglass, Terryhoogan, Tullyhugh and Tullymacann in the parish of Ballymore, and that part of the barony of Fews Upper consisting of the townland of Lisnadill.

Prior to the 1885 United Kingdom general election and from the dissolution of Parliament in 1922 the area was part of the Armagh constituency.

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.

In 1921 Sinn Féin decided to use the UK authorised elections for the Northern Ireland House of Commons and the House of Commons of Southern Ireland as a poll for the Irish Republic's Second Dáil. Armagh Mid, in republican theory, was incorporated in a four-member Dáil constituency of Armagh.

• Constituency created (1885)

• Constituency abolished (1922)

• List of UK Parliament Constituencies in Ireland and Northern Ireland
• Redistribution of Seats (Ireland) Act 1918
• List of MPs elected in the 1918 United Kingdom general election
• List of Dáil Éireann constituencies in Ireland (historic)
• Members of the 1st Dáil