SDLP leader Mark Durkan will tell his party's annual conference later today that the party was vindicated at the last Westminster election.
His leader's address is expected to argue that the SDLP is now stronger and is moving forward to new ground.
He will challenge party delegates to reclaim lost ground and make new advances based on its stance against violence. He is expected to claim the party helped force the IRA out of business and to make trenchant criticisms of Sinn Féin and the British government regarding the "on the runs" legislation which was introduced into parliament last week.
He will argue the Bill will deny victims of some 2,100 unsolved killings truth and even justice.
Mr Durkan will further challenge the Democratic Unionists over that party's stance on the Belfast Agreement.
The conference began last night with a confident and defiant speech from deputy leader Alasdair McDonnell.
The South Belfast MP told delegates the party's recent adversity would act as a catalyst for "rebuilding, renewal, rededication and a new generation of success".
He looked to the party's performance in the last local government elections, claiming that a new generation of representatives had emerged.
But it was the party's performance in last May's Westminster election which gave the lie, he claimed, to the party's detractors who said that the SDLP was finished. Citing the victories in South Belfast, Foyle and South Down, Dr McDonnell said the electorate had retained faith in the party and put paid to the dark forecasts of some in the media and rival parties.
He said the SDLP comprised "democratic constitutional republicans" who could deliver a genuinely new Ireland.
The party stood for "a new Ireland, an agreed Ireland, a better Ireland and a prosperous Ireland under the principles of democracy, equality, human rights and respect for diversity".
He said: "We in the SDLP have learned that good language in the hands of crooked people can be twisted, undermined, corrupted and tortured" and that noble terms such as "agreed Ireland" had been "abused to the point where they no longer hold any positive value or meaning and in fact because of sinister manipulation have been saturated with meanings they should not have".
He mocked unionists and Sinn Féin, denouncing their claims as parties in search of greater prosperity. Sir Reg Empey, he said, had put parades ahead of prosperity and added: "We saw what parades do for prosperity on September 10th when Belfast was shut down and so much was burned down."
Sinn Féin, he said, was interested more in its own prosperity than in the wealth of Irish people. The ideal of equality had also been similarly abused, he claimed.