Etienne Tshisekedi, who once served as prime minister of Africa's third-biggest country under Mobutu Sese Seko, has repeatedly called for the reopening of a national dialogue that produced a peace deal in 2003 that governs a political transition designed to lead to national elections by the middle of this year.
But on Monday he effectively recognised the result of last month's referendum - an overwhelming vote to adopt a new constitution - saying that although Congolese were inadequately informed on the proposed text, his party would contest the elections.
"The UDPS, faced with its responsibilities before God and before history, undertakes to lead the Congolese people desirous of peace and change to the final victory in the coming elections," Tshisekedi said.
The Union for Democracy and Social Progress (UDPS) is one of the most organised political parties in a country the size of Western Europe with a plethora of political parties and groupings, many with ethnic and regional allegiances.
The referendum last month, the first national democratic vote in the country for 40 years, delivered a resounding "yes" to a new constitution according to preliminary results, although the final tally has not yet been announced.
"The UDPS undertakes to lead the Congolese people desirous of peace and change to the final victory in the coming elections"
European Union monitors declared it free and fair despite some intimidation at polling stations and violence, during which the leader of a "no" campaign was detained by riot police.
"No" campaigners are appealing to the Supreme Court to annul the vote, arguing that the interim government's "yes" campaign received unfair support from the international community, which has a role as guarantor of the peace process and political transition.