Prime Minister Narendra Modi, whose Bharatiya Janata Party (BJP) stormed to power in 2014, campaigned hard to retain his commanding majority.
He was up against the resurgent main opposition Congress party and powerful regional rivals across the country.
Exit polls have predicted a win for Mr Modi, but analysts warn they have often been wrong in the past.
The last of seven rounds of voting over six weeks ended on Sunday and the counting of the stored ballots begins at 08:00 local time (02.30GMT.)
This election is seen as a referendum on Mr Modi, a polarising figure adored by many but also blamed for increasing divisions in India.
A party or coalition needs at last 272 seats to secure a majority in the 543-member lower house of parliament, or Lok Sabha.
In 2014, the BJP captured 282 seats - the biggest victory by any party in 30 years. The Congress, which won just 44, suffered its worst defeat.
This year, there were 900 million voters eligible to take part, making it the largest election the world had ever seen.
The fate of more than 8,000 candidates and some 670 political parties hangs on the ballot.
Results will be released in phases by the Election Commission - a picture of who is winning could emerge within hours, or it could take longer depending on how close the race is.
Final results are not expected until late on Thursday local time, or early Friday. Extra checks matching printed ballots against electronic voting machine results could delay the process.