Sanjay Singh has been in the BJP earlier.
Rajya Sabha member Sanjay Singh, who is from the former Amethi royal family, resigned from the Congress on Tuesday and said he would join the BJP on Wednesday.
Mr Singh, a Congress member of the Rajya Sabha from Assam, also resigned from the Rajya Sabha, sources said, adding that Rajya Sabha Chairman M Venkaiah Naidu has accepted his resignation.
Addressing a press conference in Delhi, the leader said he would join the BJP on Wednesday.
Mr Singh, who has been in the BJP earlier and was elected to Lok Sabha on its ticket in 90s, wields considerable influence in the Amethi region of Uttar Pradesh.
He had unsuccessful contested the recent Lok Sabha election from Sultanpur. The BJP's Maneka Gandhi had won from there.