Contreras is already serving multiple prison sentences
The head of Chile's secret police during the rule of General Augusto Pinochet has had two life terms added to the jail sentences he is serving.
A judge gave Manuel Contreras two consecutive life terms for the murder of retired army chief Carlos Prats and his wife in Buenos Aires in 1974.
Gen Prats, a symbol of opposition to the Chilean military government, had fled to Argentina.
Contreras has previously been convicted of murder, torture and kidnap.
Judge Alejandro Solis on Monday sentenced Contreras, 79, over the killing of Gen Prats and his wife Sofia Cuthbert.
They died in a car bomb attack in the Argentine capital.
"This sentence is justice for all that our parents lived through," Angelica Prats, one of the couple's daughters, told reporters.
Around 3,000 people were killed during Gen Pinochet's time in office, between 1973 and 1990.
Pinochet died in December 2006, with numerous human rights charges still pending against him.