Sri Lanka's Parliament said on Tuesday that three candidates have been nominated to replace former president Gotabaya Rajapaksa, who fled the country last week.
Acting President Ranil Wickremesinghe will face former education minister Dullas Alahapperuma, who has the backing of the main opposition, and leftist leader Anura Dissanayake in a secret ballot on Wednesday.
The three were formally nominated by legislators in a session that lasted less than 10 minutes at the tightly guarded Parliament building, AFP reported.
The winner will take charge of a bankrupt country that is in talks with the International Monetary Fund for a bailout, as its 22 million people endure severe shortages of food, fuel and medicine.
Mr Rajapaksa flew to the Maldives and then to Singapore last week and resigned over Sri Lanka's worsening economic crisis.
Opposition leader Sajith Premadasa pulled out of the race in favour of Mr Alahapperuma, a dissident member of Mr Rajapaksa's SLPP party.
Mr Wickremesinghe, 73, a veteran political operator and six-time prime minister, has the formal backing of the leadership of the SLPP, which remains the largest party in the 225-member Parliament.
Mr Dissanayake, 53, is the leader of the leftist group JVP, or People's Liberation Front, which has three seats in Parliament.
The new leader will be in office for the remainder of Mr Rajapaksa's term, which runs until November 2024.
Students and other groups plan to protest on Tuesday against Mr Wickremesinghe's bid.
Meanwhile, Mr Wickremesinghe told CNN that he aimed to stabilise the island nation's devastated economy by the end of next year.
He also accused Mr Rajapaksa's government of covering up facts.
Sri Lanka has almost concluded negotiations with the IMF, Mr Wickremesinghe's office said, following last week's declaration of a state of emergency.
The country's leaders have imposed a state of emergency several times since April, when public protests took hold against the government's handling of the economic crisis and a shortage of essential items.
Previous emergency regulations have been used to send the military to arrest and detain people, search private property and curb public protests.
Sri Lanka has been hit hard by the Covid-19 pandemic and tax cuts by the Rajapaksa government.
The tea-growing nation is in the midst of its worst economic crisis since it won independence from Britain in 1948.
Inflation of more than 50 per cent and shortages of food, fuel and medicines have brought thousands onto the streets in months of protests that culminated in Rajapaksa's ouster and forced the country to seek help from overseas.
India is willing to make more investments in Sri Lanka after supporting it with $3.8 billion this year, New Delhi's envoy in Colombo told The Indian Express newspaper.
"The idea is to respond to Sri Lanka's requests for enabling them to meet their foreign exchange crisis," said Gopal Baglay, India's high commissioner in Sri Lanka.
"We would like to continue to bring more investment into Sri Lanka because that will help create medium and long-term capacity to respond within the Sri Lankan economy."
Sri Lanka has also sought assistance from its fourth-biggest lender and India's rival, China.
A sudden surge of refugees fleeing political and economic meltdown in Sri Lanka has prompted a meeting of leading politicians in India.
The external affairs and finance ministers were due to chair a cross-party meeting on Tuesday to discuss the fallout from the Sri Lankan crisis and ways in which India can help, after significant numbers of refugees poured into the southern state of Tamil Nadu.