Tanwar had been sulking ever since he was removed from the post of Haryana Congress chief last month and had staged a protest along with hundreds of his supporters outside the residence of party's Interim President Sonia Gandhi here earlier this week, alleging wrongdoings in distribution of election tickets in the state.
He has attacked the coterie of Sonia Gandhi and has alleged that "money power" was being used in Haryana and ordinary workers were being ignored.
"After long deliberations with party workers and for reasons well known to all Congressman and public, I hereby resign from the primary membership of the @INC India," Tanwar, who was the party's Dalit face, tweeted.
He wrote a four-page letter to Sonia Gandhi, saying the Congress party is facing "existential crisis not because of its political opponents but because of internal contradictions".
He said hardworking workers, who rose from humble backgrounds and are not from political family, are not valued and "money blackmail and pressure tactics seem to work".
He said people with vested interests are killing the party and many like him are victims of it.
Haryana is going to polls on October 21.
Earlier on Friday, former Mumbai Congress chief Sanjay Nirupam also had alleged that party has been taken over by sycophants and those close to Rahul Gandhi are being sidelined deliberately.
However, Congress has rejected this charge made by Nirupam and said everybody should restrain from speaking.
( With inputs from IANS )