Colum Eastwood believes there should be a border poll in seven years' time and that the Irish government is now "moving into the space" of planning for Irish unity.
The SDLP leader said he would support a referendum on Irish unity in 2030 if the conditions are right – the first time he has specified a timeframe for the vote.
Mr Eastwood's remarks come after Taoiseach Leo Varadkar restated his belief that there will be a united Ireland in his lifetime.
The Fine Gael leader said on Thursday that he believes Ireland is "on the path to unification". He also said that in a unified Ireland there would be a significant number of people who identified as British and that "you judge the success and the quality of a country by the way it treats its minorities and that's something we're going to have to think about".
Unionists were critical of the remarks, with DUP deputy leader Gavin Robinson saying Mr Varadkar was "playing up [his] republican credentials".
But Mr Eastwood welcomed the taioseach's comments, describing them as "very good".
"I've obviously had a lot of discussions with Leo around this and with Tánaiste Micheál Martin – I think it's good that the Irish government seem to be moving into the space of planning for it (Irish unity)," he said.
"It's also good that they're coming from a perspective that the SDLP comes from, which is we need to ensure that the British and unionist tradition on the island is respected, accommodated and treated properly."
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The Foyle MP, who in the past has been reluctant to state publicly when he believes a referendum should take place, said he was "committed to doing the work so that we can win a border poll".
Speaking to The Irish News, he said he would support a border poll in 2030 if conditions were right and preparations were complete.
"That puts pressure on those of us who want to see change," he said.
"For the last couple of years, we've been working extremely hard to try to build the case and people are seeing more about that in terms of public meetings and everything else."
He called on the Irish government to re-establish the New Ireland Forum.
"That would enable all political parties on the island who want to attend to come together to discuss how a new Ireland would look and how we convince people of it.
"And I say this to unionists, we don't expect you to come and plan for something you don't want, but it'd be a good idea if unionism thought about what the United Kingdom could look like and how to make that more attractive, then we'll have a conversation in the middle a little bit democratic and free of violence."
The Foyle MP said he believed unionists "should be spending more time focused on selling the benefits of the UK rather than deriding people for even daring to talk about a united Ireland".
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