SDLP veteran Seamus Mallon’s Westminster seat will be contested by Dominic Bradley of the SDLP and Sinn Féin’s Conor Murphy.
Mr Mallon is to retire at the next election -- expected in May next year -- having served as MP for the Newry and Armagh constituency since 1986.
In his career Mr Mallon served as deputy first minister and deputy leader of the SDLP.
Mr Bradley, who was nominated at an SDLP convention in Armagh last night, faces an uphill battle to retain the seat in the face of a challenge from Sinn Féin’s presumed candidate.
In South Belfast, the SDLP’s best hope for a gain, the party selected assembly member Alasdair McDonnell.
Also last night the SDLP selected Dolores Kelly as its candidate for the constituency of Upper Bann.
In neighbouring Lagan Valley, David Trimble’s wife Daphne controversially failed in her bid to stand as a candidate.
Jeffrey Donaldson, who joined Ian Paisley’s DUP from Mr Trimble’s Ulster Unionist Party, is the sitting MP.
Mrs Trimble lost by 93 votes to 54 against UUP newcomer Basil McCrea, suggesting that divisions are continuing within the UUP despite recent defections.
In the 26 Counties, by-elections are due in the Meath and North Kildare constituencies.
A Sinn Féin selection convention in Navan selected Meath councillor Joe Reilly to run for the party in the constituency.
Reilly narrowly failed to win a seat in the last 26-County general election Speaking at Wednesday night’s election convention, he said the party was “contesting this election to win, to return the first Sinn Féin TD for Meath since Liam Mellows was elected in 1918.”