Thirty-nine others, all minors, were jailed for 10 years.
The verdict, which can be appealed, is the harshest delivered so far against non-Islamist activists amid a government crackdown on opponents overseen by President Abdel Fattah al-Sisi.
Hundreds of Islamist supporters of Mubarak’s successor, Mohamed Morsi, have been sentenced to death after often speedy trials described by the United Nations as “unprecedented in recent history”.
At Wednesday’s hearing, all 269 defendants were convicted of taking part in clashes with security forces near Cairo’s Tahrir Square in December 2011, said the judicial official who spoke on condition of anonymity.
They were also found guilty of assaulting security forces and setting alight government buildings, including a cultural centre founded in 1798 by Napoleon Bonaparte that contained more than 200,000 books.
A life sentence in Egypt is 25 years.
The defendants were also ordered to pay a combined fine of $2.2 million (1.9 million euros).
Douma, 26, rose to prominence during the 2011 uprising that drove Mubarak from power and was also a key protest leader against Morsi.
On Wednesday, dressed in a prison uniform, Douma was the sole defendant present in a metal cage inside the courtroom.
All defendants except for Douma were tried in absentia, as the authorities had released the others earlier ordering them to be present as and when required.
As the verdict was read out, Douma clapped his hands, angering Judge Mohamed Negi Shehata.
“You are not in Tahrir Square. Behave yourself and don’t talk too much or I’ll give you three more years” for contempt of court, the judge said.
Douma is already serving three years for violating a law prohibiting unlicensed protests, and was also given a three-year sentence at a previous hearing of the current trial for insulting the judiciary.
Defence lawyer Sameh Samir criticised Wednesday’s ruling.
“The judge has been biased against the defendants and their lawyers since the start of the trial,” Samir said.
“He referred the defence lawyers to prosecution, he barred us from attending the hearings and now he has issued an unprecedented verdict in Egypt’s history.”
Washington condemned the verdict.
“Mass trials and sentences run counter to the most basic democratic principles and due process under the law,” said State Department spokeswoman Jen Psaki, adding it “seems impossible that a fair review of evidence and testimony could be achieved under these circumstances.”
The European Union likewise criticised the decision, saying Egypt was violating its international human rights obligations.
“The EU calls on the Egyptian authorities to respect their international obligations, and ensure the right to a fair trial,” it said in a statement.
– ‘Verdict against the revolution’-
Douma’s brother Mohamed slammed the verdict.
“It’s an incredibly exaggerated sentence. It’s a sentence against the revolution and shows personal hatred of the judge against the revolution and the activists,” Mohamed told AFP.
“This was expected of him.”
Shehata has presided over several trials of dissidents since then army chief Sisi ousted Morsi in July 2013.
On Monday, he confirmed death sentences against 183 men convicted of killing 13 policemen in a town near Cairo, in a verdict criticised by international rights groups.
Shehata had also sentenced three Al-Jazeera journalists to between seven and 10 years in a trial that prompted international outrage.
That verdict was overturned and a retrial was ordered by an appeals court in January.
One of the three journalists, Australian Peter Greste, was freed and deported Sunday under a presidential decree.
Rights groups and critics of Sisi say authorities are using the judiciary as an arm to repress any form of dissent, including from secularists like Douma.
Amnesty International’s Hassiba Hadj Sahraoui said Monday’s death sentences were “yet another example of the bias of the Egyptian criminal justice system.”
The rights watchdog said the sentences were passed at a time when “the case against former president Hosni Mubarak, involving the killing of hundreds of protesters during the uprising, has been dropped.”
In November a court dropped murder charges against Mubarak.
If he walks free it would spur accusations against Sisi that he is reviving the Mubarak era.
Mubarak’s sons Alaa and Gamal — symbols of corruption during their father’s rule — have also been released pending a retrial.