- Baijayant Jay Panda was suspended by the party in January
- The Kendrapara lawmaker appeared to openly challenge party leadership
- Biju Janata Dal had ordered probe against him for alleged "misbehaviour"
"It's with deep anguish, hurt and sorrow that I have decided to quit the politics into which our BJD has descended," Jay Panda, 55, wrote in a letter to Naveen Patnaik, adding that he would convey his decision to the Lok Sabha Speaker.
"With the BJD and you yourself having made it abundantly clear that I am unwanted, it is only right to disassociate from it," he said in the letter that made repeated references to "Biju uncle" or Biju Patnaik, the father of Naveen Patnaik.
Mr Panda has been a parliamentarian of the BJD since 2000 and among the party's most prominent leaders from Odisha. His exit comes ahead of polls next year in Odisha, a state where the BJP has made significant in-roads, leaving the ruling party nervous.
The Kendrapara lawmaker was suspended by the party in January on "disciplinary grounds" after he appeared to openly challenge the leadership after local polls.
Last year, he was removed as the BJD's parliamentary party spokesperson over an article he wrote shortly after Panchayat or rural body polls in Odisha, alleging that the party was being run by "opportunists".
The BJP had emerged the second largest party in the polls, gaining at the cost of the BJD.
In his letter, Mr Panda wrote that things had "plumbed the absolute depths of inhumanity when neither you nor anyone from BJD turned up to pay their last respects to my father Bansidhar Panda, a close friend, supporter and associate of Biju uncle..." His father, an industrialist, died on May 22 at 87.
The party stopped short of expelling the four-time lawmaker though he alleged a conspiracy by a rival leader to remove him.
Jay Panda's attacks intensified after the BJD ordered a probe against him on the complaint of some local leaders about his "behavior".
Of the many accusations that the party has flung at Mr Panda was that he had criticised the party, praised the opposition and had even campaigned against the party's candidates in the rural body elections.
Mr Panda, who owns a large conglomerate with interests in mining, power and real estate, also said all allegations against him were false and baseless.