Séamus Mallon today urged loyalist paramilitaries to follow the IRA's lead and begin destroying weapons in his final speech as SDLP deputy leader.
He told the party's annual conference that terrorists who have waged a bloody campaign in Northern Ireland were finished.
The Ulster Defence Association and the Ulster Volunteer Force have so far refused to disarm in response to the historic move by the Provisionals.
But Mr Mallon declared: "To loyalists who continue to maim and murder, I say, your day is done.
"You have nothing to contribute until you end your violence and decommission."
The Newry and Armagh MP is stepping down as deputy leader, along with party leader John Hume, after more than two decades in the position.
He also issued a message to republican paramilitaries.
"The time has come to accept the logic of your own strategy and let go finally once and for all of any association with violence as a means of advancing a political aim."
A packed conference hall in Newcastle, Co Down, heard him recall the party's battle to achieve the policing reforms proposed by former Hong Kong governor Chris Patten.
The SDLP endorsed the new Police Service of Northern Ireland only after these changes were guaranteed during talks at Weston Park in Staffordshire earlier this year.
Support from the Irish and US governments, along with the presence of Oversight Commissioner Tom Constantine, should ensure no future shortfall, Mr Mallon said.
But he also hit out at Sinn Féin for refusing to take its seats on the Policing Board which will hold the police service to account.
"Some have rejected the new nationalist consensus on policing," he said.
"Some have chosen to go it alone. And that is were they are: themselves alone."
But the former Deputy First Minister in the Stormont power-sharing executive insisted republicans were being proved wrong.
"They said that the name would not change. And yet it has," he said.
"They say that they will not join the Policing Board. And yet, mark my words, they will." Mr Mallon sounded a note of optimism for both Northern Ireland's devolved administration and the future direction of the party he is stepping down from.
The work Stormont Ministers and Assembly members have carried out had been "exhilarating" to watch, he said.
And he urged incoming SDLP leader Mark Durkan to help drive this forward.
"I encourage our new fine leadership: have fire in your bellies, have passion in your hearts," he said.
"I know that you will carry forward the torch of truth and conviction first carried by the founders of the SDLP."
But Mr Mallon tempered his upbeat assessment with the stark reality that sectarian hatred is still rife in parts of Northern Ireland.
Turning to the ongoing dispute outside Holy Cross Primary School, he said: "On the streets of north Belfast naked sectarian territorialism victimises little schoolchildren in scenes that have shocked the world.
"The SDLP must be at the forefront of the fight against sectarianism, promoting good relations, and respect for difference and diversity."
PA