SDLP members will gather in Newry today to vote on whether the party should link up with Fianna Fáil.
Party leader Colm Eastwood said he is hopeful the move will be endorsed by the party faithful.
However, another proposal has been put forward calling for the SDLP to forge greater links with a range of political parties south of the border.
Mr Eastwood insisted the democratic foundations of the SDLP meant there was space for healthy disagreement and debate.
His comments came as Taoiseach Leo Varadkar expressed hope the SDLP's relationship with his Fine Gael party would not suffer as a consequence of the potential Fianna Fáil partnership.
Another proposal, put forward by members opposed to the Fianna Fáil deal, will instead advocate the SDLP adopt a non-exclusive approach to cross-party cooperation.
Under these terms, it would seek to forge better links with a broader range of political parties in the Republic of Ireland. Many founding grandees of the party favour the latter option.
Mr Eastwood, who met the Taoiseach in Belfast on Friday to discuss Brexit, said he was confident members would back his plan.
"What's going to happen tomorrow is there are two different proposals, one from the leadership and another proposal - I think the one from the leadership will get support. I hope it will," he said.
"The bottom line in this is we are a very democratic party, we can have a discussion, we can even disagree, we can debate and then we can come out united together - and I think that's what's going to happen tomorrow.
"We understand very well that politics has changed here, Brexit has changed everything and it is important that the SDLP are involved in that change.
"I believe that the proposal that I will be putting to the membership tomorrow is one that can get support, not just in the room but, more importantly, with the public out there, and we need to show that our values can survive and thrive in the next decade and I think that's what this is all about."
Asked if he was concerned some members would quit with party if the Fianna Fáil link-up is agreed, he said: "No, I think this is a democratic party. There have been things in the past in the SDLP that I have disagreed with.
"You have to stay in and make your arguments and then move on if you are not successful.
"The bottom line in this is the SDLP brand remains, our integrity remains, our independence remains, what we are talking about is a partnership to work together to meet the big challenges of today.
"Brexit has changed the world and if the SDLP are serious about being a player in the future we have to change, too."
Mr Varadkar, the leader of Fine Gael, was asked about the prospective link-up during his visit to Belfast.
"I think primarily that is a decision for the SDLP and I totally respect their right to make whatever decision they think is best for their party," he said.
"The only thing I would say is the Irish government has always had a very close relationship with the SDLP for decades now and my party Fine Gael has had a good relationship with the SDLP, too.
"I just hope that anything they decide to do with Fianna Fail doesn't jeopardise that into the future."