Egyptian lawmakers are to decide on the 100 members who will start work on a post-revolution constitution for the country.
Military leaders who took control after the 2011 revolution threatened to reinstate a suspended constitution from the 1970s if lawmakers couldn't settle their differences.
Some liberal lawmakers had balked over what they said was the dominance of Islamic movements in the assembly. Islamist groups like the Muslim Brotherhood's Freedom and Justice Party have come to dominate the political landscape in Egypt.
ElBaradei, a former U.N. nuclear inspector turned political reformist, said the assembly could "bury the revolution" because it "doesn't represent Egyptians," reports Egyptian news service al-Ahram.
Egyptians during the weekend choose between FJP leader Mohammed Morsi and former Egyptian Prime Minister Ahmed Shafiq in a second round of voting for president.
The role of the president may be ill-defined, however, without a formal constitution.