V. Ramesh, general secretary of the Tamil Nadu section of the Bharatiya Janata Party, died instantly in the attack by a gang inside the compound of his house in Salem, a city in the southeastern state.
The BJP, a major Indian political party at state and federal levels, was set up in 1980 to protect the rights of the majority Hindu religious group.
The attack on Ramesh, 54, took place 10 p.m., Friday, The Times of India reported.
Ramesh's death was the second slaying of a BJP functionary in the past nine months, The Daily News & Analysis reported. Dr. V. Aravind, a BJP health policy consultant, was killed in front of his clinic in Vellore city by a gang in October.
Earlier this month, S. Vellaiappan, a senior leader of Hindu Munnani -- a group set up to protect Hindu religious sites and temples -- was attacked outside a temple in Vellore.
Vellaiappan, 50, was hacked to death by a group of men on motorcycles.
The attacks on Ramesh and Vellaiappan prompted complaints from senior Tamil Nadu BJP leaders that police aren't protecting their members from assailants.
"After Hindu Munnani functionary Vellaiappan's murder in Vellore, we had requested the state police to give protection to all the BJP functionaries," Salem District BJP General Secretary R.P. Gopinath said. "But the police didn't consider our request. If they had provided protection, we wouldn't have lost our general secretary."
Hindu Munnani and the BJP are part of the Hindutva movement to promote Hindu nationalism against perceived incursions by other religions within the country of 1.2 billion people.
The country has more than 2,000 ethnic groups, including those who practice Buddhism, Jainism, Sikhism, Zoroastrianism and Christianity.
The dominant religion is Hinduism followed by Islam with around 13 percent of the population, amounting to more than 160 million people, according to the 2001 census.
The BJP, looking to wrest power from the Congress Party at federal level in next year's national election, recently chose the controversial and polarizing leader Narendra Modi to head its campaign, The Washington Post reported.
Modi, the chief minister of the western state of Gujarat, is popular among upwardly mobile, urban middle-class Indians. But he also is a reminder of the BJP's reliance on leaders who heavily promote the Hindu ideology, the Post reported.
An election win for the BJP led by Modi could be problematic for U.S.-India relations. Washington refused to grant him a visa in 2005 because of concerns about his alleged complicity in abetting religious riots in 2002, The Post report said.
But Modi denies any involvement and refuses to apologize for the riots as his ardent critics would like him to do.
In particular, human rights groups accuse Modi of not making efforts to stop mobs targeting Muslims in reprisal attacks after 58 Hindu pilgrims and activists died in a 2002 train fire that Muslims were suspected of starting. More than 1,000 people, mostly Muslims, died in the violence.