Dey, who had joined the TMC on November 25, was holding the post of West Bengal Pradesh Congress Committee (WBPCC) vice-president and was suspended by the Congress for an indefinite period for anti-party activities.
"This is a breach of party discipline and we have decided to suspend him from the party for an indefinite period," WBPCC president Pradip Bhattacharya had said.
Dey has been elected five times to the Assembly from the Shantipur constituency in Nadia district since 1991.
Speaking about the resignation, state Parliamentary Affairs Minister Partha Chatterjee said Dey's move was on moral grounds as he was looking for a fresh mandate with the change of his party.
Dey, who was present on the occasion, said he joined the TMC as he felt it was difficult to boost development process without Mamata Banerjee.