Pasupathi Pandian, founder of Devendra Kula Velalar Kootamaippu (Federation), was sitting outside his house in an isolated locality when he was attacked and killed, they said.
Police said they suspected the gang monitored the Dalit leader's movements before attacking him.
Meanwhile tension spread as news of the Dalit leader's death spread.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.