The CPM has blamed the BJP for the attack.
CPI(M) leader Badal Shill, who was critically injured in an attack in South Tripura's Rajnagar area, died while undergoing treatment at a hospital on Saturday, police said.
The opposition CPI(M) alleged that Shill, a zilla parishad candidate in the panchayat polls, was murdered by people aligned with the BJP, and called a 12-hour statewide bandh on Sunday in protest.
The state BJP said police will investigate the case and take necessary action.
South Tripura Supreintendent of Police Ashok Kumar Sinha told PTI that Shill was attacked by a group of people, who are yet to be identified, on Friday evening.
"Police visited the spot immediately after coming to know about the incident. The victim was not in a condition to tell the police anything. However, we lodged a suo motu case. An investigation is underway," he said.
Shill was attacked with 'dao' (machetes), sticks and other weapons at Rajnagar market, his family alleged.
AIG (Law and Order) Ananta Das said he died while undergoing treatment at the state-run GB Pant Hospital in Agartala.
"His post-mortem examination has been completed and the body will be handed over to his family," he said.
Shill had filed nomination papers for the panchayat elections in July 11.
CPI(M) state secretary Jitendra Chaudhury, who is also the leader of the opposition in the assembly, said Shill had received severe head injuries in the attack.
"This is not the death of Badal Shill, it is the murder of democracy by the BJP. I appeal to the people to protest this brutal murder and save the democracy," he said.
Left Front convenor Narayan Kar said the statewide bandh would begin at 6 am, and continue till 6 pm.
Addressing a press conference late in the night, BJP state spokesperson Nabendu Bhattacharjee said, "Every death causes shock. We convey heartfelt grief and sympathy to the family of Badal Shill, who died while undergoing treatment. Police will investigate the case and take necessary legal steps."
He alleged that the opposition parties were trying to create unrest in the state ahead of the panchayat elections.
"They are not being able to find candidates for the elections, and the BJP can't arrange candidates for them," he said.
Mr Bhattacharjee said the BJP will oppose the statewide shutdown because it does not support anything that hampers normal life.
"I hope the government will take all possible steps to maintain normal life on Sunday. The party will also support the government in maintaining normal life across the state," he said.
Panchayat elections will be held in the state on August 8, and the votes will be counted on August 10.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)