Mr Biswas bagged 22,234 votes.
Congress candidate Bayron Biswas is marching ahead of his rivals in minority-dominated Sagardighi assembly seat of West Bengal's Murshidabad district, where counting of votes for a by-election is underway, according to the Election Commission (EC).
Mr Biswas, who enjoys the support of the Left, was leading by 14,157 votes over TMC candidate Debashish Banerjee, EC trends revealed around 1.30 pm.
The Congress leader bagged 56,203 votes, and Banerjee 42,046 votes thus far.
Dilip Saha of the BJP secured 18,732 votes.
If Mr Biswas manages to win the by-election, also being seen as a prestige fight for state Congress president Adhir Chowdhury in his home district, it will be the party's first seat in the current Assembly, the strength of which is 294.
"I am confident about my victory. People here are fed up with the corruption and misrule of the TMC," Mr Biswas said.
Mr Chowdhury said the party's victory is dedicated to the joint fight by the Congress and the Left supporters in the district.
"The result proves that Mamata Banerjee is not invincible. We will re-establish democracy in West Bengal. We have fought this election in alliance with the Left, and it is a victory of the coalition. People have reposed their faith in us and discarded both the TMC and the BJP," Mr Chowdhury told reporters.
By-poll was necessitated following the death of state minister Subrata Saha in December last year. The TMC, which had been winning the seat since 2011, secured a margin of more than 50,000 votes in the 2021 assembly elections.
Apart from more than 60 per cent minority population, the rural constituency has around 18.5 per cent Scheduled Caste and 6.5 per cent Scheduled Tribe population.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)