Guha took to politics at an early age and was a close aide to Mamata Banerjee. Between 2001 and 2003, on instructions from Mamata Banerjee, Guha intervened in the defense of squatters that were being evicted from the banks of Tolly's Nullah and Gobindapur railway colony.
Guha was first elected to the West Bengal Legislative Assembly in 2001 from the Satgachhia (Vidhan Sabha constituency) on an All India Trinamool Congress ticket. She defeated Gokul Bairagi of the Communist Party of India (Marxist) by about 6,000 votes. Her victory was significant as the seat had been held for five terms by Chief Minister Jyoti Basu, since 1977, but Basu decided not to contest the 2001 election for health reasons.
In the 2006 assembly election Guha defeated Kabita Kayal of the Communist Party of India (Marxist) by about 6,000 votes. She was elected as the first women deputy speaker of the West Bengal Legislative Assembly.