Adolfo Scilingo, 58, the first official of Argentina’s ex-military junta to be tried abroad, was found guilty of crimes against humanity, arbitrary detention and torture, including throwing political prisoners to their death from aircraft.
Presiding judge Fernando Garcia Nicolas said Scilingo, who came to Spain in October 1997, could only serve a maximum of 30 years under Spanish law, and he has already served four of these.
Buenos Aires agreed in 2003 that Spain could try Scilingo as there were no equivalent charges against him in his home country.
Scilingo had been charged in the deaths of 30 people in the notorious “death flights” in which drugged regime opponents were thrown alive into the ocean from planes.
He was given 21 years for each of the 30 victims and another 10 years for other atrocities.
The Spanish prosecutors called the verdict “historic” but expressed regret the defendant, whose trial began on January 14, had not been found guilty of the more serious charge of genocide.
In all, 30,000 political prisoners are believed to have disappeared during the right-wing military dictatorship that ruled Argentina from 1976 to 1983.
Scilingo was also accused of involvement in abuses committed at the ESMA naval mechanics school in Buenos Aires.
Some 5,000 people disappeared at the ESMA during the “dirty war”.
At his trial he described how prisoners had passed through ESMA and said he was involved with “action groups” whose job it was to kidnap, torture and then dispose of detainees.
He also said he was aware of the existence of a centre where babies were taken away from their mothers and handed to naval families.
“There was a systematic plan to make people disappear and steal children so that they did not grow up in the households of ‘subversives’,” said Maria Isabel Mariani, a witness who testified at his trial.
Human rights organisations estimate around 500 babies were taken from their families.