SINN Féin leader Mary Lou McDonald has described the Brexit deal as the "least worst option".
Mrs McDonald said ultimately Brexit - which was opposed by a majority of voters in Northern Ireland - was "fundamentally wrong" and "undemocratic".
"It will hamper the economy, agreements and restrict the rights of citizens," she said.
"The agreement endorsed between the EU27 and the British government does not resolve Brexit.
"It is the least worst option - there is no good Brexit."
The Sinn Féin leader added that "it must be clear that under no scenario will there be a hardening of the border in Ireland or the abandonment of the Good Friday Agreement".
Last weekend, writing in The Irish News, Mrs McDonald gave a cautious welcome to the text presented by British Prime Minister Theresa May just days earlier but said that there were "still issues of concern and clarification required".
"It (the backstop) provides the bottom line and is our insurance policy against the worst excesses of Brexit, which we know will be a disaster for this country," she wrote.
"The backstop is not perfect and neither is the withdrawal agreement."
Meanwhile, the Sinn Féin MEP Martin Anderson has accused the Taoiseach Leo Varadkar of leaving Irish citizens from the north behind by not allowing them to vote in European elections after Brexit.
The Republic is to get two additional MEPs following Brexit, bringing its total number to 13, while the north will lose its existing three seats.
Ms Anderson told RTÉ: "The Irish government are one of the few member states who deprive their nationals from the right to vote who don't reside in the member states - 22 other member states do this.
"The Irish government could do this at the flick of a pen if they so wanted."
