Modi's Bharatiya Janata Party (BJP) and its allies are forecast to win 279 seats in the lower house of parliament, the poll conducted by Hansa Research for the NDTV news channel showed. A majority of 272 seats is needed to form a government.
Modi has electrified India's general election, the world's largest ever democratic exercise, with a media-savvy campaign that has hinged on promises to kickstart a slowing economy and create jobs.
Yet he is seen as a polarising figure, described by critics as an autocrat with Hindu supremacist views.
Indian elections are notoriously hard to predict and polls conducted both before and after voting have a patchy record. The country's five weeks of staggered voting ended on Monday and results are due on Friday.
Six exit polls released earlier this week forecast results ranging from 249 to 340 seats for the BJP-led alliance. The group will be in a strong position to lure regional parties to form a coalition government even if its seat tally comes in at the bottom end of that range, political analysts say.
Several exit polls over-estimated the BJP's seat share in the last two general elections in 2004 and 2009. The ruling Congress party fell short of a majority but went on to form coalition governments on both occasions.
Congress faces an uphill struggle to stay in power this year because of public anger over the economic slowdown and a string of corruption scandals.
The ruling party and its allies were forecast to pick up 103 seats in the NDTV poll. Congress alone was projected winning just 79 seats, which would be the worst showing ever for the party led by the Nehru-Gandhi dynasty.