Enrique Jose Berthier, a former army captain, was also sentenced to 10 years in prison for handing over the baby to the couple.
Al Jazeera's Lucia Newman, reporting from Buenos Aires, said that Sampallo was told from a very young age that Pinto and Rivas were her adoptive parents.
"From then on she started investigating. About 10 years ago, she went to a genetic blood bank set up by the Argentine government to try to identify some of these children," she said.
"When she discovered that she had been lied to all along, she proceeded to sue them."
The court ordered that Sampallo's identity card be destroyed as it bears the false name of Eugenia Violeta Rivas.
Many pregnant women who were arrested when Argentina's military government cracked down on left-wing activists and dissenters gave birth in detention and were never seen again.
Around 500 "stolen babies" were given to families close to the ruling party.
About 88 of them have also been able to trace their true identities with the help of the Grandmothers of the Plaza de Mayo, a human rights group founded in 1977 to try to find babies stolen during the "Dirty War" and reunite them with their biological families.
Activists from the group said that the three defendants should have received the maximum sentence of 25 years.
"We do not agree with the sentence," Rosa de Roisinblit, the vice president of Grandmothers of the Plaza de Mayo, said.
"We were hoping for something more just for our grandchildren.
"In the United States and other countries, a stolen child is almost akin to murder, and here it's nothing," she said.
Tomas Ojea Quintana, Sampallo's lawyer, said he would appeal for longer prisoner terms for the three defendants.