"Udayan Guha has joined the Trinamool Congress. He is a good organiser. He will function as a secretary of the TMC," Chief Minister Mamata Banerjee said after arriving from Delhi.
Guha, MLA from Dinhata in Coochbehar district, would contest the next Assembly election from the same constituency, Banerjee said.
Guha had last week resigned from all posts in Forward Bloc and praised Mamata Banerjee.
He had time and again expressed his displeasure over the functioning of the party's top leadership.
Guha, who had met Banerjee in the Assembly premises last month had stated, "I had gone to meet her in public view. I have nothing to hide. I had not gone to meet her wearing veil. I admire Mamata Banerjee personally.