In a letter to All India Trinamool Congress general secretary Abhishek Banerjee, the former Rajya Sabha member said he had offered many suggestions to party supremo and West Bengal Chief Minister Mamata Banerjee to make TMC acceptable in Assam, but those were "not implemented".
Prashant Kishor became aware over time that the Congress would never completely accept him.
Ripun Bora, an ex-minister of Assam Minister, quit the Congress and joined the TMC a week ago in the presence of the party's national general secretary, Abhishek Banerjee.
Bora, as a joint candidate of the opposition parties in Assam, had unsuccessfully contested the recent Rajya Sabha election.
The opposition 'Grand Alliance' comprising the Congress, AIUDF and eight other parties won 50 seats.