Bhaskar Jadhav had started his career with Shiv Sena but later switched to Mr Pawar's party.
The exodus from the Nationalist Congress Party continued on Friday, with another senior leader quitting the party to join the Shiv Sena. Bhaskar Jadhav, a former Maharashtra president of the Sharad Pawar-led party, resigned as an MLA. He later joined the ruling party in the presence of its chief Uddhav Thackeray.
Mr Jadhav, 62, comes from the Konkan region of Maharashtra, which is the Shiv Sena's stronghold. In the 2009 assembly elections, the NCP had fielded him as a candidate from Guhagar constituency, where he had won by 12,000 votes, defeating Ramdas Kadam.
Mr Jadhav had started his career with Shiv Sena but later switched to Mr Pawar's party.
Since the BJP and Shiv Sena's stellar performance in the Lok Sabha elections, several important leaders of the NCP-Congress alliance have switched sides. A few days ago, three Congress leaders had quit within 24 hours, including actor-turned-politician Urmila Matondkar, who had joined the party before the national election.
Ms Matondkar had contested from the North Mumbai parliamentary seat unsuccessfully.
On the same day, senior NCP leader from Navi Mumbai Ganesh Naik also quit the party and joined the BJP.
Both Bhaskar Jadhav and Ganesh Naik are considered politically influential. With the series of resignations, the chances of Mr Pawar's party in the upcoming Maharashtra elections are likely to take a hit.
Earlier this year, Madhukar Pichad-- another senior NCP leader-- had quit the party and joined the BJP along with his son.
The state will go polls in October.