The merger between Democratic Left and the Labour Party was an opportunity to reform Irish politics, the DL leader, Mr Proinsias De Rossa, told the special one-day conference in Dublin called to decide on the proposal.
"This opportunity arises specifically from the people's endorsement of the democratic settlement of the Northern Ireland conflict. It has ended division on the left about the national question and we no longer comply with the De Valera dictum that Labour must wait."
With the political message "Democratic Left - New Politics - New Century" on the platform behind him, he told the last Democratic Left conference that "to credibly argue for reform we must first transform ourselves, transform our ideas, our politics and our organisation." The Belfast Agreement dwarfed "all the petty squabbling which passes for politics in our State. That Agreement is, in my view, a thing of beauty, crafted by ordinary politicians practising the art of politics at its best."
Democratic Left's agreement with Labour "does not obliterate our differences or traditions nor does it dissolve them. It accommodates them and creates the space for something new to evolve and thereby strengthens the Left to face a new century with new politics."
The party leader, who described the conference logo as a "rose with a missing petal, returning home" said that no document could be described as socialist simply because it claimed to be so - a reference to the absence of the word "socialism" in the new agreement. "And the reverse is also true. No document can be dismissed as not socialist, simply because it does not carry the label `socialist'.
"We must judge people, parties and documents by the values they espouse and the policies based on those values which they pursue."
He said that the poor, the homeless, the badly paid, the family with sick children, those with a disability and their families "are not interested in our historical animosities." What they wanted to see was leadership, courage and determination to right the wrongs that they lived with.
Democratic Left and Labour were the only parties "who have demonstrated the courage to embrace change. Uniquely in modern Irish politics our two parties are coming together with diverse traditions, but similar values and objectives to offer to the Irish people a new choice, a new way of making politics."
The Left was weak in Ireland "and Labour has traditionally been very weak." He said that the critique of Irish society, "the programmes we develop based on that critique and on our socialist values, the organisational reconstruction and the political alliances we make in pursuit of our ideals are for us all to decide and pursue with passion."
They would not be drawn, however, from old socialist manuals or threadbare rhetoric. "They will be new ideas suited to the new times we live in."
After the vote, the party leader said he was "clearly delighted" that members had supported the decision to enter negotiations and to back the agreement.
Opening the conference earlier the party's Wicklow TD, Ms Liz McManus, said that politics was often a messy, untidy business. "Differences are confronted because otherwise no movement can occur," she said.
It was "collective strength that makes us indestructible, not party names or who is leader or how many public representatives we have. It is the very core that enables us to build on reality as on a rock. It is what binds us together and connects us to others beyond our party, even to those beyond our reach until now."
The former Cork TD, Ms Kathleen Lynch, told the delegates they would have to decide whether they would allow the conservative parties to dominate Irish politics for decades to come.
"Why is it that the vote of the left in Ireland has never gone above 22 per cent? Why is it that Cork, the biggest county in the country, and the location of the second city, does not have a single left TD and that its present 20 TDs are drawn exclusively from the ranks of Fianna Fail and Fine Gael?" she asked.
"The challenge facing members of both parties is to see if they can rise above traditional rivalries and put their own particular interest to one side in order to create a genuinely new political alternative to the traditional dominance of Irish politics by Fianna Fail and Fine Gael."