Gerry Adams has said there is no "absolute protection" for the Union from the British government.
The Sinn Fein President also 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 destabilising, 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.
Democratic Unionist leader Arlene Foster has said the prospect of a border poll is not sensible while Northern Ireland Secretary James Brokenshire has said the conditions for calling such a poll have not been satisfied.
The British and Irish governments are expected to make a fresh bid to kickstart stalled powersharing talks soon.
Mrs Foster has called for a return to direct rule from Westminster if no deal can be reached.
She accused Sinn Fein 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 Fein 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 Sinn Fein's Martin McGuinness resigned as deputy first minister at Stormont. He died last March.