Thirty-nine other defendants, all minors, were sentenced to 10 years in prison.
All 269 defendants were found guilty of taking part in clashes with security forces near Cairo's Tahrir Square in December 2011, the sources said.
A life sentence in Egypt is for 25 years.
Wednesday's ruling, which can be appealed, is the harshest court order delivered so far against non-Islamist activists amid a government crackdown overseen by President Abdel Fattah al Sisi.
Hundreds of supporters of Mubarak's successor, Mohamed Morsi, have been sentenced to death after often speedy trials.
Douma rose to prominence during the 2011 uprising that ousted Mubarak and was also a key protest leader against Morsi.
He is already serving three years for violating a law prohibiting protests without a permit.
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