Mr John Hume said the Nelson amounted to was an attack on the peace process.
"This was not just an attack on a courageous young woman who was committed to the pursuit of human rights and justice, but also an attack on the peace process. Those behind the attack have nothing to offer our society."
Mr Martin McGuinness, Sinn Fein's chief negotiator, claimed the attack followed the same pattern as the murder of Mr Pat Finucane, the Belfast solicitor shot dead by masked men in his home 10 years ago. "It is public knowledge that her life has been threatened on a number of occasions by the RUC Special Branch."
Mr Paul Murphy, the North's Development Minister, said the attack was sinister, cowardly and despicable. "While it is too early to speculate on who was responsible for this horrific incident, we will leave no stone unturned in the effort to bring the perpetrators of this evil crime to justice."
The deputy leader of the Ulster Unionist Party, Mr John Taylor, condemned the murder on behalf of the party "without reservation" and said the killing was wrong. "While unionists would have disagreed with Rosemary Nelson's views and actions, murder can never be condoned."
The DUP leader, the Rev Ian Paisley, "unequivocally" denounced the attack. "A mother is dead and her children have been left without a mother." He added that until there was paramilitary decommissioning of arms and explosives there would never be real peace.
The Alliance Party deputy leader, Mr Seamus Close, said those behind the attack wished to blow apart the prospects of peace and political stability. "They will be defeated by the positive outworkings of all democrats."
Ms Brid Rodgers, the SDLP Assembly member for Upper Bann, commended Mrs Nelson for her work with the Garvaghy residents in Portadown and her representation of the family of Mr Robert Hamill, who was kicked to death by a loyalist gang in the town two years ago.
"She defended the basic human rights of a vulnerable and exposedcommunity," Ms Rodgers said.
A Sinn Fein Assembly member, Ms Dara O'Hagan, a friend of the solicitor, claimed there were those within the military establishment who were intent on silencing Mrs Nelson. "This was an attack carried out by experienced people and was not the work of amateur loyalist groups."
The Women's Coalition has urged people to line up behind Mrs Nelson's aspirations and ensure that her death reinforces "the principles of justice, by which she lived."
The North's human rights group, the Committee on the Administration of Justice, has called for an independent investigation into the murder and said it would be "untenable" for the RUC to head the inquiry.
The president of the Northern Ireland Law Society, Mrs Catherine Dixon, said the attack was cowardly and a blatant attempt to intimidate the profession. "Solicitors have worked over many years of the Troubles to provide the best possible service to the entire community."
Mr Brian Fee, chairman of the Northern Ireland Bar Council, said Mrs Nelson was a "respected colleague" who upheld the highest professional standards. The Northern Ireland Human Rights Commission deplored the "senseless waste" of Mrs Nelson, whom it described as "a valued legal adviser".
In a statement, Republican Sinn Fein claimed there was "British crown forces involvement . . . probably using loyalist death squads as their instruments."