The by-elections were held on November 25.
After trailing the BJP in the initial rounds of counting, the Trinamool Congress bounced back in Kaliaganj, where its candidate Tapan Deb Singha emerged victorious with a 2,304-vote margin.
Bharatiya Janata Party's Kamal Chandra Sarkar took the second position, while Left Front-backed Congress candidate Dhitasree Roy finished a distant third.
The bypoll was necessitated by the death of Roy's father Congress legislator Pramathanath Roy.
In Kharagpur Sadar, Trinamool candidate Pradip Sarkar was leading by 18,707 votes. Left Front-backed Congress contestant Chittaranjan Mondal, who had surged ahead after the opening round, was lying a distant third.
BJP aspirant Prem Chandra Jha was running second.
Kharagpur Sadar in West Midnapore district had elected state BJP president Dilip Ghosh in the 2016 Assembly polls. The constituency went to the hustings after Ghosh got elected to the Lok Sabha from the Midnapore constituency earlier this year.
The Trinamool has also left behind its opponents in Karimpur, where its nominee Bimalendu Sinha Roy was ahead of his nearest rival state BJP vice president Jay Prakash Majumder by 23,603 votes.
Karimpur constituency in Nadia district had to go for the bypoll as its lawmaker Trinamool's Mahua Moitra won the Lok Sabha battle from Krishnanagar.
Congress backed CPI-M candidate Golam Rabbi lagged far behind in the third position.
The Left Front and the Congress formed an alliance for the bypolls, but failed to cut much ice.
The results have come as a major disappointment for the BJP which got massive leads in the Assembly segments of Kharagpur Sadar and Kaliaganj, where its heavyweight candidates triumphed in the Lok Sabha polls.
While Ghosh got a huge lead of over 45,000 from Kharagpur Sadar, present Union Minister Debosree Chowdhury had established a massive margin of about 57,000 votes in Kaliaganj on way to winning the Raiganj parliamentary seat.
Chowdhury and Ghosh had been camping in their respective strongholds as they led vigorous campaigns, making the election a prestige battle for the BJP.
The Trinamool's winning candidate from Murshidabad Lok Sabha seat Abu Taher Khan had given his party around 14,000 vote lead in Karimpur during the general election.
( With inputs from IANS )