Mohammed al-Zawahri was arrested at a police checkpoint in August 2013, days after security forces stormed a Cairo sit-in camp by supporters of ousted President Mohammed Morsi, killing more than 600 people.
The younger al-Zawahri was the leader of an extremist group and was a close ally of Morsi, who hails from the Muslim Brotherhood, AP reported.
He was charged with the formation and leadership of a terrorist organization and with attempting to overthrow the government by force.
In its Thursday ruling, the court sentenced 10 of al-Zawahri's 67 co-defendants to death and handed life sentences to 32 others.