Banerjee, who became the first woman Chief Minister of the state in May, had consistently been elected to the Lok Sabha since 1984, except in 1989.
Her victory significantly coincided with a verdict of the Calcutta High Court upholding the Singur land act as constitutional and valid.
The ruling TC added another feather in its cap as its candidate A T M Abdullah wrested Basirhat North assembly seat in North 24 Paraganas district trouncing Subid Ali Gazi of CPI(M) by 30,941 votes, officials said.
Banerjee, who had given up her Railway portfolio, to become the chief minister, had to contest the polls within the stipulated six months after assuming office.
She had skipped the assembly contest in April-May on grounds that she needed to campaign for the party to oust the 34-year-old Left Front regime.
While Banerjee was expected to win the poll, all eyes were on her victory margin.
While a high voter turnout of 80.35 per cent was recorded in Basirhat North, it was as low as 44.88 per cent in Bhowanipur in Sunday's bypoll. In the May election Bhowanipore had recorded 63 per cent voting. Banerjee had polled 73,635 votes and Mukherjee 19422 votes.