Suzette Jordan was offered a lift by five men as she left a night club in Kolkata city's Park Street in February 2012.
She was gang-raped inside the moving car for several hours before being thrown out onto the street.
Despite conservative attitudes which often blame the victim for rape, the single mother of two daughters chose to reveal her identity in order to give courage to others - winning praise from gender rights activists around the world.
She died in March after contracting meningitis.
Public prosecutor Sarbani Roy said Interpol notices had been issued for two other accused who were still on the run.
"The magistrate pronounced the judgment today, he will announce the quantum of punishment tomorrow. I am happy for our victory and sorry for the conviction," Roy told reporters in Kolkata, West Bengal state's capital city.
Under Indian law, the minimum sentence for gang rape is 10 years' imprisonment.
Opposition political parties called on West Bengal Chief Minister Mamta Banerjee to apologize after she claimed in 2012 that Jordan's reporting of the rape was false and politically motivated to tarnish the government's reputation.
Banerjee welcomed the verdict in the case, which has come to be known as the "Park Street Rape", but made no mention of her previous comments.
"It is a good judgment, I welcome it," Banerjee was quoted as saying in local media.
