Dulal Biswas, a panchayat leader of Nadia district's Bagula, was fatally shot multiple times inside the party office on Sunday evening.
"Biswas suffered multiple bullet injuries in in the abdomen. He was rushed to the Krishnanagar Hospital, where he was declared dead," said a senior district police official.
Mr Biswas' son, who was present outside the party office during the incident, claimed to have recognised a few people to be active members of local Bharatiya Janata Party and Left Front units.
"I was standing in front of the party office when 10-12 men came on bike and instantly started firing at my father. I recognised a few of them. They are active members of CPI-M and BJP units," he said.
The state Trinamool leadership accused the BJP of active involvement in the murder and said no one involved in the incident would be spared by the administration.
"This is an attempt to politically weaken the Trinamool Congress in the area. We are all beside the bereaved family and the party activists here. The administration would strictly handle the issue," said party Secretary General Partha Chatterjee.
"This is a cowardly act... The BJP is doing the politics of terror. No one will be spared in this incident," said Trinamool Congress MP Abhishek Banerjee.
Refuting the allegation, BJP state president Dilip Ghosh alleged the Trinamool Congress was trying to cover up its shortcomings and internal feud by putting the blame on BJP and claimed that the people of the state won't believe in these false allegations.