On 1 November 1956, under States Reorganisation Act, 1956, a portion of the Purnea district east of the river Mahananda and the Purulia sub-district of the Manbhum district in the south (except Char Thana) were transferred from Bihar to West Bengal.[1] Thus, assembly constituencies in West Bengal increased from 187 (238 seats) to 195 (252 seats) during 1957 assembly elections.
The election was won by the Indian National Congress, who got a majority of its own in the assembly. The communists became the largest opposition party.