More than 30 close associates of Muammar Gaddafi were tried for suppressing peaceful protests during the uprising.
Saif al-Islam Gaddafi was not present in court and gave evidence via video link.
He is being held by a former rebel group from the town of Zintan that refuses to hand him over.
Former head of intelligence for the Gaddafi regime, Abdullah al-Senussi, is among those also facing death by firing squad, as is former PM Baghdadi al-Mahmoudi.
Saif al-Islam Gaddafi is also wanted by the International Criminal Court on charges of war crimes and crimes against humanity.
Prosecutors say that he was part of his father’s plans to “quell, by all means, the civilian demonstrations against the Gaddafi regime”.
Saif al-Islam Gaddafi will be given the right to appeal against the death sentence.
The trial, which opened in 2014, has been dogged by criticism from human rights agencies, who are concerned about the fairness of Libya’s judicial system.
Eight other ex-officials received life sentences and seven were given jail terms of 12 years each, said chief investigator Sadiq al-Sur. Four were acquitted.
The defendants were accused of incitement to violence and murdering protesters during the uprising that eventually toppled Muammar Gaddafi.
Since Gaddafi’s death Libya has been plagued by instability, and currently has no single government.
Instead two warring factions each claim to run the country. An internationally recognized parliament is based in Tobruk, while Tripoli is held by rivals Libya Dawn.
Saif al-Islam Gaddafi has been held in the mountainous town of Zintan since the end of the war, by rebels who are allied to the Tobruk-based government.
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