The condemned men, charged with "leading a group known as the Helwan Brigades", were found guilty of having committed acts of terror, including opening fire at a police vehicle, the judicial source told AFP.
The men were convicted in relation to events that took place between August 2013 and February 2015 -- a period that saw a spike in attacks, particularly targeting security forces, following the military ouster of Islamist president Mohamed Morsi.
The court also handed down jail sentences to 205 others in the same case, ranging from 10 years to life imprisonment.
Subject to appeal, the verdicts drew condemnation from Amnesty International, which described them as an "insult to justice" resulting from "grossly unfair proceedings."
President Abdel Fattah al-Sisi has presided over a mass crackdown on Islamists and dissidents, jailing thousands.
Egyptian courts have routinely handed down death sentences or long jail terms after mass trials that have drawn condemnation from the United Nations and rights organizations.
"This was a mass trial of more than 200 people," Amnesty International's Amna Guellali said in a statement Tuesday, alleging that the case was "marred by enforced disappearances and torture", prisoners being kept in "cruel and inhuman conditions" and "flagrant trial breaches".
"Authorities must quash the verdict and order the release of detainees, most of whom had been held for over two years in pretrial detention in contravention of Egyptian law," Guellali added.
Egypt carried out the third highest number of known executions in the world last year, after China and Iran, according to Amnesty.