Ranil Wickremesinghe, a political veteran who has been prime minister of the country five times before, faces the daunting task of leading his country through its worst economic crisis since independence.
Economic mismanagement, the COVID-19 pandemic and rising energy costs following Russia's invasion of Ukraine have drained state coffers, meaning Sri Lanka is running low on fuel and essential medicines and facing daily power blackouts.
Rajapaksa, whose elder brother Wickremesinghe replaced as prime minister, has called country-wide curfews and given security forces sweeping powers to shoot at anyone involved in looting or putting people's lives at risk.
Mahinda Rajapaksa, who resigned on Monday, has gone into hiding on a naval base and the president has warned of the risk of all-out anarchy.
Ordinary people have grown increasingly frustrated at disruptions to normal life.
"We have hit the bottom economically," said Nimal Jayantha, an autorickshaw driver queuing for petrol earlier on Thursday after the curfew was lifted.
"I don't have the time to do my job. By the time I stay in the fuel queue and get petrol, curfew will be imposed. I will have to go home without any money."
As well as dealing with mass protests, Wickremesinghe must unite a fractured parliament to agree on a way out of a crisis in which inflation has soared and foreign reserves dwindled.
"He has said from the beginning, parliament needs to come together to provide a solution to the crisis," Dinouk Colombage, media secretary from Wickremesinghe's opposition United National Party, told Reuters.
"He is no stranger to dealing with economic and political challenges, having done so multiple times before."
