Roy's exit comes amid growing speculation that Mamata Banerjee may be losing her grip over the party's parliamentarians, mirroring the rebellion that has already surfaced within the Trinamool Congress legislative wing in West Bengal.
'Party failed to read people's mood'
Announcing his resignation, Roy said he was among several leaders who had been sidelined within the party and accused the leadership of failing to understand public sentiment.
"The party has failed to take the correct approach. It has not even acknowledged the poll defeat," Roy said.
"Downfall is imminent when a party is unable to read people's mind," he added.
Claiming that loyal leaders had been ignored for years, Roy said: "I was among several honest leaders who were sidelined within the party for years."
Roy has also alleged institutional corruption under the TMC rule.
"The party had no ideology ever but was driven by programmes to oust the Left. Coming into power, the party was immersed into corruption," he said.
More resignations on the cards?
Several media reports have claimed that Bengali actor and newly elected Rajya Sabha MP Koel Mallick may also step down from the Upper House, adding to the uncertainty within the party.
Meanwhile, a group of disgruntled TMC parliamentarians is reportedly holding a separate meeting in the national capital, signalling a possible revolt against the party leadership.
Revolt spreads to Assembly
The turmoil is not limited to Parliament.
In West Bengal, expelled TMC MLA Ritabrata Banerjee was nominated as the Leader of Opposition by nearly 60 MLAs, overturning Mamata Banerjee's choice of senior leader Sovandeb Chattopadhyay.
The development exposed deep divisions within the party and effectively split the defeated camp inside the Assembly.
BJP ends 15-year TMC rule
The Bharatiya Janata Party (BJP) swept to power in West Bengal for the first time, winning 208 seats in the Assembly elections.
The TMC was reduced to 80 seats, bringing an end to Mamata Banerjee's uninterrupted 15-year rule in the state.