NASA intends to establishing an initiative to review the constitution to safeguard devolution.
This follows a meeting on Thursday between its principals led by Raila Odinga and other elected politicians.
CEO Norman Magaya has said the coalition will take its proposal to county assemblies for approval, then mobilise grassroots leaders.
He said the People's Assembly, recently called for by Raila, will comprise elected political leaders, religious, trade union and civil society leaders, as well as women and youth organisations.
"It is to constitute a convention to be held in Nairobi to discuss and determine the pathway to democracy and constitutionalism and to restore legality and the rule of law," he said.
Magaya said during the meeting, Raila and co-principals Musalia Mudavadi and Moses Wetang'ula briefed coalition members on its plan to form a special committee to review the constitution.
He said the committee will review the performance of, among other institutions, national security organs and the electoral body.
Raila formed the People's Assembly on Tuesday after reiterating the election was a sham and that only 3.5 million people voted.
Raila, who earlier announced a national resistance movement, said NASA will carry on with its restoration of democracy
in line with the law.
"There will be a broad-based forum of elected leaders and sector including workers, civil society, religious leaders and economic interest
groups," he said at Okoa Kenya.
The ODM leader said the assembly will exist until a legitimate president is installed.