Egyptian law requires the grand mufti to be consulted on death sentence cases, although his opinion is not legally binding and those convicted still have the right to appeal.
Those found guilty were among 713 defendants on trial for killing policemen and vandalising property during 2013 clashes between security forces and supporters of ousted president Mohamed Morsi.
Senior Brotherhood members Mohamed el-Baltagui, Issam al-Aryan and Safwat Hijazi were in the dock, while 31 others were tried in absentia.
Egypt sentences 21 to death for planning terror attacks
Also on trial was prominent photojournalist Mahmud Abu Zeid, widely known as Shawkan, who in May received UNESCO's Press Freedom Prize. The court postponed a verdict on his and other cases.
On August 14, 2013, one of the bloodiest days in Egypt's modern history, a month after the army ousted Morsi, police moved to disperse a sprawling protest camp at Rabaa al-Adawiya square in Cairo.
About 700 people were killed within hours at Rabaa al-Adawiya and the capital's Nahda Square where another sit-in was being held.
Egypt court sentences diva over Nile hygiene remarks
Hundreds more were killed in street clashes with police over several months after the August carnage and mass arrests were carried out.
Global rights groups Amnesty International and Human Rights Watch say at least 40,000 people were arrested within the first year of Morsi's ouster on July 3, 2013.
Egypt's courts have sentenced to death or lengthy jail terms hundreds of people after speedy mass trials, including Morsi and several leaders of his Brotherhood movement.
Many have appealed and won retrials but 26 executions have been carried out.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ