Polling stations opened at 7 am (01:30 GMT) on Saturday in a poll widely seen as a referendum on his successor Ranil Wickremesinghe, who has restored some stability through austerity policies backed by the International Monetary Fund (IMF), Al Jazeera reported.
The measures, including tax hikes, have left millions struggling to make ends meet and are unpopular with many voters.
Wickremesinghe, who is expected to lose to one of his two rivals, was unrepentant as he addressed his final campaign rally in Colombo.
“We must continue with reforms to end bankruptcy,” 75-year-old Wickremesinghe, a veteran politician who has been prime minister multiple times, told his final rally in Colombo this week.
“Decide if you want to go back to the period of terror, or progress.”
The economic crisis has boosted support for Anura Kumara Dissanayake, the leader of the Janatha Vimukthi Peramuna (JVP), despite his party’s violent past. The 55-year-old has promised to change the island’s “corrupt” political culture.
Fellow opposition leader Sajith Premadasa, the son of a former president assassinated in 1993 during the country’s decades-long civil war, is also expected to make a strong showing.
About 17 million Sri Lankans are eligible to vote and will rank three candidates in order of preference on the ballot paper. A record 38 candidates are vying for the presidency.