1983–1997: The District of Armagh, and 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.

1997–present: The District of Armagh, and 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.

The constituency is majority nationalist, though initially on its creation in 1983 Jim Nicholson of the Ulster Unionist Party won the seat due to the nationalist vote being divided between the Social Democratic and Labour Party and Sinn Féin.

In 1986 Nicholson, along with all the other unionist MPs, resigned his seat in protest over the Anglo-Irish Agreement and stood in a by-election to provide voters the opportunity to decide on it.

Mallon stood down at the 2005 general election fearing the loss of his seat as was widely predicted among political pundits, the seat subsequently fell to Sinn Féin with Murphy out polling the SDLP by almost 8000 votes.