They claimed that Sen never resorted to violence or incited anyone else to do so. On the contrary, as a doctor and a human rights activist he stood up in defence of the rights of downtrodden, said a statement signed by Romila Thapar, Prabhat Patnaik, Ashok Mitra and Mushirul Hasan among others.
"Yet he has been handed down this sentence whose savagery is unbelievable," it said.
Sen, Naxal ideologue Narayan Sanyal and Kolkata businessman Piyush Guha were sentenced to life imprisonment last Friday for colluding with Maoists to establish a network to fight the state.
58-year-old Sen, a paediatrician by training and vice-president of People's Union of Civil Liberties, had been accused of acting as courier for Sanyal, who was in jail, by carrying his messages and letters to the underground Maoists.
The intellectuals said, "Such an action on the part of the State in the name of preserving the Constitutional order will only serve to undermine that Constitutional order itself.
"It will inevitably raise the thought in the minds of many that an order within which the activities of a person like Dr Sen can be held to be seditious is not worth defending," the statement said.
Noting that such an impression must be avoided, they said, the damage done by this "shocking" verdict must be undone and sought his immediate release till the end of the appeal.
Sen's supporters have also started an online campaign for his release by posting a petition on the Internet which will be sent to President Pratibha Patil. Close to 3,500 people have signed the petition so far.
"The charges against Dr Sen, of allegedly aiding outlawed Maoist rebels in Chhattisgarh, have not been corroborated by any of the witnesses or evidence produced in court so far.
"On the contrary there have been numerous instances of the prosecution resorting to use of fabricated documents and contradictory testimonies to press its case," petition claimed.