Gerry Adams has said there is no "absolute protection" for the union from the British government.
The Sinn Féin President attacked the DUP's pro-Brexit and pro-union position.
Unionists have warned that previous calls for a referendum on a united Ireland are divisive and destabilizing, and want to ensure Northern Ireland is treated no differently from the rest of the UK after separation from the EU.
Mr Adams added: "The rationale behind the DUP stance is that it is focused on maintaining the union, but there is no longer any absolute protection for the union from British governments the way there used to be.
"British government involvement in our affairs will end when a majority vote for that."
The 1998 Good Friday Agreement includes the principle of consent, which affirms the legitimacy of the aspiration to a united Ireland while recognising the current wish of the majority in Northern Ireland to remain part of the United Kingdom.
It says it is for the people of both parts of the island alone to exercise self-determination on the basis of consent.
DUP leader Arlene Foster has said the prospect of a border poll is not sensible while Northern Secretary James Brokenshire has said the conditions for calling such a poll have not been satisfied.
The Irish and British governments are expected to make a fresh bid to kickstart stalled power-sharing talks soon.
Mrs Foster has called for a return to direct rule from Westminster if no deal can be reached.
She accused Sinn Féin of prioritising issues such as a stand-alone Irish language act over jobs, schools and hospitals.
Mr Adams said: "Michelle O'Neill and our negotiating team stand ready to engage positively in any talks.
"Sinn Féin wants the 20th anniversary of the Good Friday Agreement to be a positive point in the history of our island.
"The call by the DUP leader for a return to British direct rule flies in the face of her party's devolutionist position.
"But it also reflects a refusal to face realities."
This month marks a year since Martin McGuinness resigned as deputy first minister at Stormont.
DUP East Antrim MP Sammy Wilson said the impasse was entirely a result of Sinn Féin's actions in collapsing the executive as he lambasted Mr Adams.
"If he really is concerned about the poor, homeless and sick then he will join with other parties in returning to the executive without preconditions rather than the mindless pursuit of squandering money on an Irish Language Act at all costs.
"Since his rhetoric at the start of 2018 is no different to the end of 2017 the prospects for restoring devolution look bleak unless the UK government removes the veto Sinn Féin currently holds by ensuring that if they refuse to participate then other parties can get on with the job of providing government for Northern Ireland."