Pramod Mahajan, a former federal telecommunications minister and high-profile general secretary of the Hindu nationalist party, was shot at his home in the financial capital of Mumbai on April 22.
"He finally succumbed to the bullet injuries," said Anupam Verma, spokesman of Hinduja Hospital.
Mahajan, 56, was hit by three bullets. Doctors at the Mumbai hospital had performed three surgeries to try to revive him.
He is survived by his wife, a son and a daughter.
Mahajan's younger brother, Pravin, surrendered to police shortly after the shooting. Police say Pravin shot Mahajan three times because he resented the latter’s success and felt ignored and humiliated by him.
The younger brother's lawyer claims his client is "deranged."
Mahajan was part of the BJP's "Generation Next" and known for his organisational skills. A key backroom manager of his party, he was also close to both its top leaders, Atal Behari Vajpayee, the former prime minister, and Lal Krishna Advani, his deputy.
He was known for his oratory skill and was seen as a possible future head of the party.
"The party is in a shock after his untimely death. He had a big role in holding together the BJP-led coalition," senior BJP leader V.K. Malhotra told reporters in New Delhi.
"This is a loss not just for the BJP but for the whole country - there were few leaders of his dynamism and his promise," Yaswant Sinha, former foreign minister in the BJP-led government which lost power 2004, told NDTV television