Julio Simon was convicted of kidnapping and torturing Jose Poblete and his wife, Gertrudis Hlaczik, and kidnapping their eight-month-old daughter, Claudia, during the country's bloody 1976-1983 military rule.
The baby was eventually handed over to a military family and illegally adopted. The child's biological parents were never seen again and are presumed dead.
As many as 30,000 suspected leftists were kidnapped and killed during the dictatorship, according to rights groups.
Victims' relatives present in courtroom broke out in applause as the sentence was read.
Dozens of human rights activists gathered outside the Buenos Aires courthouse cheered the decision against Simon, who is also known as "Turco Julian."
"This a historic day, one that opens the way for more trials," said Estela de Carlotto, the president of human rights group Grandmothers of the Plaza de Mayo.
The first such sentence since amnesty laws were overturned in 2003 found the former police officer "criminally responsible for illegal deprivations of freedoms aggravated by its repetition, forcible suffering to the politically persecuted and the abduction of a child."
Argentine President Nestor Kirchner began campaigning in 2003 to lift amnesties protecting military and police officials involved in rights abuses, and he annulled a decree preventing their extradition from Argentina.
Argentina's Supreme Court in 2005 ruled unconstitutional a blanket amnesty that benefited about 1,000 military staff accused of state terrorism during Argentina's last dictatorship in the case of Poblete and Hlaczik.
Their daughter Claudia, 22 years later, discovered her identity and Simon was charged, but could not be convicted because of the amnesty law, until last year's Supreme Court decision.
Two high-ranking officials had already been jailed in the kidnappings of some 500 children of dissidents, a crime not covered in the amnesty: Former general Jorge Videla and former admiral Emilio Massera, who are both in ill health.
The 2005 Supreme Court decision breathed life into survivors' cases against the military, which ruthlessly clamped down on opponents and their children, engaging in torture and leaving some 30,000 people missing and presumed dead, rights groups say.
The decision allowed courts to subpoena dozens in the military, active or retired, who are suspected of having tortured prisoners. Many were allegedly tortured in the presence of their loved ones, siblings or children.
The two amnesty laws were decreed in 1986 and 1987, under Radical Party president Raul Alfonsin. One law granted enlisted men and officers protection from prosecution if they claimed that they had merely followed orders in committing abuses. The other law granted an amnesty outright to the commanders who gave the orders.
Tens of thousands of regime opponents were tortured after the 1976 military coup and before democracy returned in 1983. Many were flung alive from helicopters into the ocean.