Julo Simon, nicknamed Turco Julian, was convicted on Friday of kidnapping and torturing handicapped Chilean Jose Poblete and his wife, Gertrudis Hlaczik, during the military government's rule between 1976 and 1983.
He was also found guilty of kidnapping the couple's baby daughter, Claudia, who was eight-months-old at the time, November 28, 1978.
The baby was later handed over to a military family and illegally adopted.
Poblete and his wife were never seen again and are presumed dead.
Victims' relatives and representatives of human rights groups present in the Buenos Aires courtroom broke out in applause as the sentence was read.
The sentence found Simon "criminally responsible for illegal deprivations of freedoms aggravated by its repetition, forcible suffering to the politically persecuted and the abduction of a child".
Human rights advocates hailed the ruling as a step towards obtaining justice.
"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.
Nestor Kirchner, the Argentinian president, initiated moves in 2003 to remove amnesties protecting military and police officials involved in rights abuses, and annulled a decree preventing their extradition from Argentina.
In June 2005, the Supreme Court ruled unconstitutional two amnesty laws passed in the 1980s.
"This a historic day, one that opens the way for more trials"
Estela de Carlotto, Grandmothers of the Plaza de Mayo
Argentina's military rulers seized power on March 24, 1976, beginning seven years of rule in which prosecutors say they waged a systematic crackdown on perceived dissidents known as the Dirty War.
An official report said some 13,000 people disappeared during that period while human rights groups put the figure at around 30,000.
Suspected government opponents were abducted, often in the middle of the night, and taken to secret detention centres where they were believed to be tortured and eventually killed.
Poblete had arrived in Argentina in 1971 after losing both legs in a train accident in his native Chile.
The authorities said he was active in a leftist group in Buenos Aires and met his wife, a psychology student. The couple had a daughter in March 1978, and were captured eight months later.
Claudia discovered her identity 22 years later and Simon was charged, but could not be convicted then because of the amnesty law.
Two high-ranking officials, former general Jorge Videla and former admiral Emilio Massera, had already been jailed for the kidnappings of about 500 children of dissidents, a crime not covered in the amnesty. Both are in ill health.