The group issued a statement a day earlier expressing dismay over the "unjust" sentence given to Binayak Sen, a 60-year-old doctor.
In December a court found Mr Sen and two others guilty of sedition and sentenced them to life in prison.
Amnesty International said the charges were politically motivated and the trial didn't meet international standards. Mr Sen has appealed against his conviction.
He worked in villages in the backward Chhattisgarh state, rallying tribal people to fight for their social and political rights, often angering authorities.
"Dr Sen is an exceptional, courageous and selfless colleague, dedicated to helping those in India who are least able to help themselves," the Nobel laureates said in their statement, posted on a website campaigning for Mr Sen's release.
Dr. Sen's wife Dr. Ilina Sen expressed her disappointment at the court verdict. She felt there were fair grounds for bail. “We shall file a special leave petition in the Supreme Court as soon as possible,” she said
"It appears that the court has relied on the prosecution's argument of culpability by association," said Ramesh Gopalakrishnan of Amnesty International, adding he was yet to read the 34-page judgment. "The prosecution's argument was based on thin evidence and did not establish the chain of events from Dr. Sen's association with Narayan Sanyal to any actual acts of violence," he said.
In a statement prior to his conviction, Dr. Sen said he was being persecuted for highlighting police atrocities in Chhattisgarh and for opposing the Salwa Judum, a controversial State-supported anti-Maoist campaign.
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