Egyptian President Mohammed Morsi, in one of his first official acts, ordered the Parliament to reconvene. The Supreme Council of Armed Forces had ruled to disband the assembly after a high court found part of the election for Parliament this year was unconstitutional.
The court said its decisions weren't subject to appeal.
The Muslim Brotherhood's Freedom and Justice Party and al-Nour, a Salafist party, held mass demonstrations in downtown Cairo to express their support for Morsi.
Cleric Mazhar Shaeen said following Friday prayers the country's judicial leaders shouldn't move to "abort the revolution," Egyptian news service al-Ahram reports.
Political leaders in Egypt have expressed frustration over the pace of reforms in the country since a 2011 revolution unseated Hosni Mubarak after three decades in power.
U.S. Secretary of State Hillary Clinton arrives Saturday in Cairo to express support for the democratic transition under way in Egypt. Her European counterpart, Catherine Ashton, is expected to travel to the region next week.