Sri Lanka's six-time prime minister Ranil Wickremesinghe was sworn in Thursday as president of the crisis-hit South Asian nation, his office said.
Wickremesinghe, 73, who was elected by legislators on Wednesday, took his oath of office before chief justice Jayantha Jayasuriya at the tightly-guarded parliament complex, a statement from his office said.
Former public administration minister Dinesh Gunawardena, a schoolmate of Wickremesinghe, is tipped to become prime minister.
Gunawardena and Wickremesinghe have known each other since the age of three and studied together at the prestigious Royal College of Colombo.
Gunawardena is a trade union leader and represents a small nationalist party allied with the ousted Rajapaksa's SLPP party.
"There will be a few MPs from the main opposition joining the cabinet," a source close to Wickremesinghe said, adding that he was keen to ensure a rainbow coalition.
Worshipping at a Buddhist temple on Wednesday evening after his election by the 225-member parliament, Wickremesinghe vowed tough action against troublemakers.
"We will deal with them firmly according to the law. We will not allow a minority of protesters to suppress the aspirations of the silent majority clamouring for a change in the political system."
Protesters who stormed Rajapaksa's palace and toppled him earlier this month have accused Wickremesinghe of being a proxy of the once-powerful family.
"I am not a friend of the Rajapaksas," he told reporters at the Gangaramaya temple. "I am a friend of the people."