Former MLA and senior leader Ashok Kumar Panigrahi resigned from the BJP on Saturday nine days ahead of the bypoll to the Bijepur Assembly constituency.
The bypoll is scheduled to be held on October 21. Mr Panigrahi said he quit the party for being ignored by senior leaders.
"I felt neglected and ignored by party's state leadership. Therefore, I resigned from the BJP," he said, adding that he has sent his resignation letter to the party's state president.
Mr Panigrahi was elected to the Odisha Assembly on a BJD ticket in 2000. He had joined the BJP after resigning from the BJD ahead of the 2018 bypolls and had become the party's candidate.
He was defeated in the elections, while BJD candidate Rita Sahu, won the Bijepur seat in the bypolls.
Ms Sahu had contested the by-election in 2018 as the ruling BJD candidate and won the Bijepur seat after death of her husband and then Congress MLA Subal Sahu.
"Though Union minister Dharmendra Pradhan played a key role in making me a BJP candidate in the 2018 bypolls, he did not keep any contact after my defeat," Panigrahi said.
Asked whether he would join the BJD again, Panigrahi said, "I am not going to join any party before the October 21 bypolls."
He, however, said he would not sit idle during the campaigning.
"I will not hesitate to campaign against the BJP candidate if my supporters put pressure on me," he said.
The BJP has fielded Sanat Gartia as its candidate for the Bijepur seat this time.
Gartia has been pitted against BJD's Rita Sahu and Congress nominee Dillip Kumar Panda.
Mr Panigrahi's resignation may come as a setback for the BJP as the former MLA hails from Bijepur assembly segment and has a good number of supporters.
The bypoll was necessitated after Chief Minister Naveen Patnaik, who won from both Bijepur and Hinjili Assembly Constituencies this year, vacated the Bijepur seat.
While polling in Bijepur Assembly constituency will be held on October 21, the counting of votes is scheduled to be conducted on October 24.