Berenson, 40, has been held since her 1995 arrest on charges of collaborating with the Tupac Amaru Revolutionary Movement, a Marxist rebel group, in an alleged plot to attack the Peruvian Congress, the BBC reported Wednesday. Berenson has consistently denied the charges against her.
A military court found Berenson guilty in 1996 and sentenced her to life in prison. The sentence was subsequently reduced to 20 years after she was convicted on lesser charges.
Berenson had dropped out of the Massachusetts Institute of Technology and traveled to Central and South America, the BBC said. She married another prisoner, Anibal Apari, in 2003 and the couple had a son last year.
Apari, who is also Berenson's lawyer, was serving a 13-year sentence for his involvement with Tupac Amaru.
Berenson's release was not expected to occur before Wednesday, The New York Times reported. Peruvian government officials said they would appeal the ruling granting her release, the newspaper said.
"This is a day I'll cherish for the rest of my life," Berenson's father, Mark Berenson, told the Times.