Here are the next key steps in the poll, in which 17 million Sri Lankans are eligible to choose the Indian Ocean nation's tenth president for a five-year term.
CAMPAIGN RALLIES
Official campaigns begin after the election panel approves candidates, with inaugural rallies nationwide. President Ranil Wickremesinghe's rally on Saturday in the historic city of Anuradhapura will be the first of about 100 he plans. His key rivals are also expected to hold dozens of rallies each.
MANIFESTO ANNOUNCEMENTS
In the coming weeks, the candidates are expected to publish their positions on efforts to chart Sri Lanka's way out of its financial crisis since running out of foreign reserves, sending its economy into freefall and defaulting on foreign debt in 2022.
Other key policy issues will be corruption and improvement of living standards.
END OF CAMPAIGNING
By law candidates must wrap up campaigns 24 hours before election day.
ELECTION PROCESS
Sri Lanka's first-past-the-post system allows voters to cast three preferential votes for their chosen candidates, with the candidate securing 50% of the votes or more declared winner.
If no candidate gets 50% in the first round there is a legal provision for a run-off to tally preferential votes for the two frontrunners, but that has not happened since the introduction of the voting system four decades ago.
VOTING AND COUNTING
Votes are cast in thousands of polling stations amid tight security, to be counted by government employees after polling ends, supervised by Election Commission officials, election monitors and representatives of candidates.
DECLARATION OF RESULTS
The Election Commission will formally announce the winner, probably on Sept. 22, who goes on take the presidential oath, usually on the same day, and appoint a new cabinet.
