Bhunia, who will file his nominations for the Rajya Sabha elections on Wednesday, submitted his resignation as Congress MLA to the Speaker of West Bengal state Assembly.
Bhunia, a Congress MLA since 1982 and also the West Bengal Pradesh Congress Committee president from 2010 to 2011, switched over to TMC last year after he was suspended by Congress following his refusal to step down as chairman of the Public Accounts Committee (PAC).
"Today all relations with Congress has formally come to an end. I had a long association with Congress. But, I am happy that Trinamool Congress supremo Mamata Banerjee has entrusted me with a responsibility. I will try my best to fulfil my responsibilities and duties," Bhunia told reporters.