He said the NCRC was "willing to listen to views and remarks by the NDA delegation on the draft constitution," following a meeting with a senior official of the NDA in Khartoum.
"The NDA participation will be a qualitative addition to the Commission as well as to the political life in the Sudan," said Yassir Arman, also a spokesman for the NCRC.
Their participation will bring to over 200 the number of participants in the commission, which the NDA had refused to join pending the signing of a final peace agreement with the Sudanese government.
Khartoum and the NDA, a grouping of several opposition groups, signed the agreement on Saturday.
It paved the way for the NDA to participate in the NCRC and in a national unity government to be formed by July 9, under an agreement former southern rebel, the Sudan People's Liberation Movement (SPLM), signed with the government in January in Nairobi, Kenya.
The agreement, which ended nearly two decades of south-north conflict that left more than 1.5 million people dead and displaced some four million, also called for the passing of a constitution to govern the country during a six-year interim period.
Sudan's ruling party and its peace partner, the SPLM, inaugurated the NCRC on April 30 after failing to convince the majority of opposition groups, including the NDA and Umma party, to sign up.
The Umma party of former prime minister Sadiq al-Mahdi and 10 other groups charged that the makeup of the NCRC was not representative of the country's political landscape.
They also objected to the insistence of the NC and SPLM on applying general power-sharing quotas agreed upon in the Nairobi peace agreement, which give them 52 percent and 28 percent of the seats respectively.