Trinamool Congress MLA Satyajit Biswas was shot dead by unidentified assailants in West Bengal's Nadia district on Saturday evening.
According to police, the incident happened when Biswas was ofering prayers during Saraswati puja celebrations at Phoolbari in Jalpaiguri district.
The culprits immediately fled from the spot after killing the lawmaker.
Biswas, 41, was present with state minister Ratna Ghosh and Trinamool District President Gourishankar Dutta when he was shot dead.
He was then immediately rushed to a local hospital where doctors declared him "brought dead".
Biswas was representing Krishnaganj constituency in the assembly.
According to the police, Biswas was shot multiple times from a close range when he was coming down the podium after attending the event.
A high-level inquiry has been ordered into the killing, the police said.
Meanwhile, TMC blamed BJP for the attack and accused its leaders of "stoking tension" in the area.
Partha Chatterjee, General Secretary, TMC said, "Satyajit Biswas our MLA was a dear colleague. Words fail me. Recently BJP leaders tried to stoke tension in the area. This was an orchestrated plan to eliminate him, designed to try and benefit BJP. People will give a befitting reply to perpetrators of this dastardly act."
"Those who have killed him will not be spared. Those responsible for his death will be brought to book. BJP is responsible for this shocking death. There are some traitors who have killed him. Chief Minister Mamata Banerjee has directed the party leaders to stand beside the family of the victim", he added.
BJP state president Dilip Ghosh denied the charges and claimed that the killing might be the result of infighting in the TMC.
"The allegations are baseless. The BJP is not at all involved in the case. Those who are blaming us are actually trying to hide their own sins," Ghosh said. Senior BJP leader Mukul Roy also termed the allegations as baseless.