Roy said he would quit the party's working committee today and resign as Rajya Sabha MP as well as from the party's primary membership after Durga Puja.
"I was one the signatories when the party was founded. I am announcing with a heavy heart that I will resign from the party's working committee today.
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"And after the Durga Puja festival, I will resign from the Rajya Sabha and also from the primary membership of the party," Roy said at a press conference.
Roy, whose relationship with the leadership has been strained of late, said he would give an explanation on why he was leaving the party and why he was "forced to do so" after Durga Puja.
The TMC, the ruling party in West Bengal, had last week censured Roy for allegedly hobnobbing with BJP leaders and said it was keeping a close watch on him.
Asked whether he would join the BJP in days to come, Roy said, "Whatever I have to say. I will say it after Durga Puja. But I would like to mention that people of Bengal don't like political controversies during Durga Puja,".
Once the second-in-command in the TMC after Chief Minister Mamata Banerjee, Roy was absent from an event to unveil the Durga Puja edition of the TMC mouthpiece, Jago Bangla, on September 19.
Banerjee and the entire TMC top brass, barring Roy, was present at the event.
Roy was recently removed as the TMC vice president after the party decided to restructure its committee.
He was earlier removed as the party's in-charge of Tripura, where the TMC was steadily making inroads till its members switched over to the BJP earlier this year.