Michelle O'Neill has called for an Irish unity referendum within five years.
Addressing republicans at an Easter Rising commemoration in Belfast's Milltown Cemetery, the Sinn Fein vice president said: "Ending partition has now taken on a new dynamic because of Brexit.
"Brexit exposes the undemocratic nature of partition.
"Sinn Fein believes there should be a referendum vote on Irish unity within the next five years."
Her wide-ranging speech also touched on the Good Friday Agreement, which marks its 20th anniversary this month, and the current Stormont impasse.
Many of those participating in yesterday's event wore historical military-style uniforms and carried replica firearms.
Mrs 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.
"However, Arlene Foster and the DUP leadership failed to deliver on this and chose to withdraw from the talks and collapse the process.
"For now they are under no pressure from the British Government to move, because Theresa May is in hock to the DUP.
"It's no surprise the British Government has put its self-interest before ours.
"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 functioning 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 the Troubles.
Meanwhile, speaking at the south Down Easter Rising commemoration in Castlewellan yesterday, Sinn Fein national chairperson Declan Kearney MLA said: "Republicans seek authentic reconciliation with unionism.
"A new phase of the peace process based upon reconciliation and healing must be our future.
"Sinn Fein looks beyond present recrimination towards reconciliation.
"Our project is to achieve an Ireland with rights, equality, fraternity and anti-sectarianism at its core.
"We aim to be in government both north and south.
"But we will only accept political institutions in the north which are based upon genuine power-sharing and parity of esteem."