1983-1997: The District of Newry and Mourne wards of Ballybot, Belleek, Bessbrook, Camlough, Creggan, Crossmaglen, Daisy Hill, Derrymore, Drumalane, Drumgullion, Fathom, Forkhill, Newtownhamilton, St Mary's, St Patrick's, Tullyhappy, and Windsor Hill; and the District of Armagh.
1997-present: The District of Newry and Mourne wards of Ballybot, Bessbrook, Camlough, Creggan, Crossmaglen, Daisy Hill, Derrymore, Drumgullion, Drumalane, Fathom, Forkhill, Newtownhamilton, Silver Bridge, St Mary's, St Patrick's, Tullyhappy, and Windsor Hill; and the District of Armagh.
The seat was created in boundary changes in 1983, as part of an expansion of Northern Ireland's constituencies from 12 to 17, and was predominantly made up from the old Armagh constituency with the addition of Newry town from the old South Down constituency. In 1995, the Boundary Commission originally proposed to abolish the seat with the Armagh district joining most of Dungannon in a new 'Blackwater' constituency with the rest becoming part of a new Newry and Mourne constituency. This was strongly opposed during the local enquiries and the eventual boundary review left the seat unchanged. It contains the entirety of Armagh district and the Newry half of Newry and Mourne district.
The unionist vote in the constituency has declined somewhat in recent years, with the shift being more marked as both the Ulster Unionist Party and the Democratic Unionist Party now stand. The main attention has been upon the rise of the Sinn Féin vote. In the 2001 they surged forward, cutting Mallon's majority drastically, as well as heavily outpolling the SDLP in the equivalent area local elections held on the same day. Then in the 2003 Assembly election Sinn Féin won three seats to the SDLP's one. Mallon stood down at the 2005 general election and, as widely predicted, the seat fell to Sinn Féin.