The Trinamool Congress on Sunday officially announced Chief Minister Mamata Banerjee as its candidate for the by-election in Bhabanipur.
TMC's campaign in the seat in south Kolkata is already underway with the Election Commission announcing the by-poll on Saturday, following a request from the state government to avoid a constitutional crisis.
Banerjee, who lost the election in Nandigram, has to win this by-poll to retain her chief minister's post.
The Bharatiya Janata Party, Congress, and Communist Party of India (Marxist)-led Left Front are yet to announce their candidates for the by-poll.
The by-poll will be held on September 30 along with the elections to two seats in the Murshidabad district -- Samserganj and Jangipur where polling could not be held during the eight-phase assembly elections earlier this year.
The counting of votes will take place on October 3.
Jakir Hossain is the TMC candidate in the Jangipur seat, while Amirul Islam is contesting as the party's candidate from Samserganj.
Veteran politician Sovandeb Chattopadhyay stepped down as the TMC MLA of Bhabanipur, allowing Banerjee a chance to become a member of the state legislative assembly by fighting the by-poll.
Chattopadhyay had defeated BJP's actor-politician Rudranil Ghosh by around 28,000 votes from Bhabanipur.
Banerjee had won from Bhabanipur twice since 2011.
She had moved out of her traditional seat to fight in Nandigram during the assembly polls earlier this year but lost to his former close aide Suvendu Adhikari who contested on a BJP ticket.
Adhikari is now the Leader of Opposition in the West Bengal Assembly.
The notification for the Bhabanipur by-poll will be issued on September 6, beginning the nomination process. September 13 is the last date of filing nominations, while scrutiny of papers will take place on September 14.
September 16 is the last date to withdraw from the electoral battle.
According to an Election Commission statement, the West Bengal chief secretary had urged that in view of administrative exigencies and public interest and to avoid a vacuum in the state, by-elections for Bhabanipur, from where CM Mamata Banerjee intends to contest elections, may be conducted.
She has to become a member of the state legislature by November 5.