A further three defendants were given life sentences for the gang-rape of the victim.
The court in Kolkata handed down the sentences following their conviction on Thursday. The 21-year-old woman was targeted as she walked home after an exam in 2013 in eastern West Bengal state.
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Senior public prosecutor Anindya Raut told AFP: "It was a gruesome crime, a rarest of the rarest case."
Judge Sanchita Sarkar handed down the verdicts in a packed court which included the victim's family.
"I award the death sentence to three convicts on charges of gang-rape and murder of the student and life imprisonment to three others for gang rape, criminal conspiracy and causing disappearance of evidence," Sarkar said.
Scores of activists and people from the victim's home village were at court chanting slogans against the convicts and demanding death for all of them.
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Extra police officers were deployed outside the court following a scuffle Thursday between police and protesters who tried to enter the court complex.
"Justice has failed us as two of the accused were acquitted and three were awarded life sentences," the victim's brother told AFP.
The woman, who cannot be named for legal reasons, was grabbed after getting off the bus before being dragged to a nearby abandoned farm.
The gang attacked her as she returned from the university to her home in a village, 50 kilometres (30 miles) northeast of Kolkata, on June 2013.
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She was found gagged and laying in a pool of blood in a field the next morning. Evidence showed she had been repeatedly raped.
Two of the eight accused were acquitted for lack of evidence by the court.
The attack triggered anger in West Bengal state and came just months after the fatal gang-rape of a student in Delhi in December 2012 that shone a global spotlight on violence against women in India.
The 2012 incident led to an overhaul of India's rape laws including speeding up of trials and tougher penalties for offenders, but high numbers of assaults persist.
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