Colum Eastwood has delivered a rallying call to SDLP supporters in South Belfast.
The constituency is expected to come down to a tight race between his SDLP candidate Claire Hanna and the DUP’s Emma Little Pengelly.
Ms Hanna’s campaign received a boost when both Sinn Fein and the Green Party announced they would step aside to back her as a Remain candidate.
The Alliance Party is also running in the constituency on a Remain ticket, with Paula Bradshaw as its candidate.
SDLP leader Mr Eastwood described Ms Hanna as “by far and away the best candidate to take this seat for the Remain side” but cautioned against over confidence.
“No matter what others might tell you, the DUP can still win this seat, I’ve looked the bar charts, seen the graphs, looked at the leaflets, lots of stuff has been said and it happens in every single election,” he said.
“But the only thing that counts are votes in a ballot box.
“Pundits don’t count, polls don’t count, bookies’ odds don’t count for anything – if you don’t come out and cast your vote for Claire Hanna you’re going to have a DUP MP.
“That’s what is at stake here.”
Mr Eastwood, who is running as a candidate in Foyle, added: “We will walk as many streets, get as wet, get as cold as we have to get and get as cold as we have to get to make sure we have as many Remainers elected to the next Parliament as possible.”
Ms Hanna paid tribute to Mr Eastwood for taking a night off from his own campaigning to support her in South Belfast.
She said: “We know this is a very very tight election, it is a two-horse race between a Remainer and a Brexiter, it is a two-horse race between a shared future and a scared future.
“That’s a message we need to say, we need every single vote, we need them out, that’s a message that I will be bringing to doors every waking hour of every day between now and December 12.”
Green Party leader Clare Bailey also attended the event to formally endorse Ms Hanna after indicating last week her party will stand aside in the constituency.
Mr Eastwood commended her attendance, adding it “says something about how important this election is”.
“We have to unite to defeat this crazy Brexit, I’m delighted that we have that broad support and that we are offering that broad support as well in other constituencies,” he said.
Ms Hanna also received endorsement from youth participation group Our Future Our Choice NI.
The group’s co-founder Doire Finn said the group will announce the other candidates they plan to back later this week.
Earlier, anti-abortion campaigners held a demonstration outside the event.
Precious Life director Bernie Smyth was among a number of protesters who held banners aloft at the door of the event.
Ms Smyth said they were held the demonstration in response to Ms Hanna’s pro-choice stance on the abortion issue.