Fianna Fáil and the SDLP are expected to announce an official partnership later today.
Details will be revealed in Belfast by party Leaders Michaél Martin and Colum Eastwood.
They are expected to stop short of announcing a full merger and instead are likely to canvass for each other in elections, work on all-island affairs and partner up on European matters.
However, Former Sinn Féin TD Peadar Tóibín says it may be too little, too late for Fianna Fáil and the SDLP.
Mr Tóibín said: "For 20 years Fianna Fáil have been talking about standing in Northern Ireland.
"Now the idea that it would take a party 20 years dithering to work whether they should simply represent Irish people in all the counties in Ireland is illogical, especially if the party pretends to be an All-Ireland party."