Michelle O'Neill has called for an Irish unity referendum within five years.
Addressing republicans at an Easter commemoration in Belfast's Milltown cemetery, the Sinn Féin deputy leader said: "Ending partition has now taken on a new dynamic because of Brexit...
"Because Brexit exposes the undemocratic nature of partition.
Her wide-ranging speech also touched on the Good Friday Agreement, which marks its 20th anniversary this month, and the current Stormont impasse.
Ms O'Neill said republicans had engaged in political talks for over a year and repeated criticisms of the DUP for walking away.
She said: "The leadership of both parties reached a fair and balanced accommodation - a draft agreement
- which we felt could address our concerns, and provide a basis to restore the Executive without further delay.
"For now, they are under no pressure from the British Government to move, because Theresa May is
in hock to the DUP.
"But let's be very clear here today the rights issues are not going away.
"We are not going away."
Northern Ireland has been without a government since January 2017.
The devolved Stormont institutions fell when Martin McGuinness resigned amid a row over a botched
green energy scheme.
However divisions between the two biggest parties have widened to include Irish language rights,
the ban on gay marriage and dealing with the legacy of Northern Ireland's toxic past.
Meanwhile, Ms O'Neill also spoke about the recent violence in Palestine and called for the Irish government to expel the Israeli ambassador.
"So the Taoiseach should send the Israeli ambassador home and move immediately to recognise the state of Palestine."