Astiz, now 59 and nicknamed the Blond Angel of Death, had already been tried and sentenced to life in absentia by a French court for the murder of Alice Domon and Leonie Duquet, who disappeared in December 1977. Ten human rights activists were also abducted at the time.
On Wednesday, he was sentenced for murders including those of the two Frenchwomen; the founder of the Mothers of the Plaza de Mayo, Azucena Villaflor; and journalist Rodolfo Walsh, among others.
Official figures say 9,000 people were kidnapped, tortured and killed in what became known as Argentina's "Dirty War" against what the military believed or perceived to be leftists. Many believe the real number killed is closer to 30,000.
The court "sentences Alfredo Astiz to life imprisonment, for abductions, torture and homicide," the sentence read in part, in his case, part of a mass prosecution against 18 former military staff, mostly sailors.
On May 6, a government lawyer called for a life sentence for Astiz, who had been accused of participating in the nuns' kidnapping while he worked for GT332 (Task Force 332) based at the ESMA Naval Mechanics School in Buenos Aires.
Duquet and four other women were allegedly thrown alive from an airplane as it flew high above the South Atlantic.
The bodies of Duquet and the four Argentine women were discovered in 2005 at a seaside cemetery buried under headstones that read "NN," or no name. Locals buried the remains after the tide washed their bodies ashore.
Hundreds of dictatorship-era victims are known to have been thrown alive into the ocean on similar so-called "death flights."