The agreement between the Association of Southeast Asian Nations (ASEAN) and India, its seventh-largest trading partner, covers billions of dollars in trade and a market of 1.7 billion people.
Singapore's Minister for Trade and Industry Lim Hng Kiang and India's Minister for Commerce and Industry Kamal Nath announced the deal during an ASEAN meeting in the city-state.
Nath expressed India's "deep satisfaction" at the conclusion of the pact, which followed six years of talks.
"This is an important milestone for our region," he said.
ASEAN and India have set a target for total trade to reach 50 billion US dollars by 2010 from 38 billion dollars currently, Nath added.
The Southeast Asian bloc of about 550 million people is forging free trade pacts with key regional economies, including China and India, to ensure it does not become economically sidelined