He alleged that he was punished for "precipitating" the situation by "aggressively" speaking against Modi, which made it "untenable" for Nitish Kumar to stay in the NDA.
Tiwari, in a press statement, said that in hindsight "I feel Nitish did not want to sincerely confront Narendra Modi."
He said the best time to walk out of the NDA was when Nitish Kumar had cancelled a dinner for Narendra Modi and other BJP leaders in Patna (in 2009).
"Why did he (Kumar) retrace his steps after going this far" Tiwari said.
Had he decided to part ways with BJP at that time, JD(U) could have got majority in 2010 Assembly elections alone and BJP could not have gained the strength it ultimately got, he added.
"He missed the best time to walk out of NDA," Tiwari said claiming he had advised Nitish Kumar for this.
Tiwari, who had gone to JD(U) from RJD of Lalu Prasad in 2008 and was made a Rajya Sabha member then, said after 2010Assembly elections Kumar continued with his anti-Narendra Modi policy.
"I aggressively opposed Narendra Modi and RSS...I was removed from the post of party spokesman to weaken my anti-Modi voice," he said.
Tiwari said recently the CM held a core committee meeting of the party in which state JD(U) President Bashistha Narayan Singh and several ministers were present.
"At the end of the meeting, the CM accused me and Agriculture Minister Narendra Singh, of speaking against Modi at the party convention at Rajgir on October 28-29, which made it untenable for Kumar to stay in NDA," he said.
"As a result, in the new committee was constituted by the party President Sharad Yadav, I was neither re-appointed spokesman nor General Secretary," he added.
After being denied re-nomination to Rajya Sabha,
Tiwari has been firing salvos at Kumar regularly. Tiwari and two others N K Singh and Shabir Ali were told to contest Lok Sabha elections instead. While Ali agreed to do so, Tiwari and Singh have declined.
The CM in his reaction to Tiwari's remarks against him had said recently "this is my fate."