The move ended the 51-day crisis which started in October.

President Maithripala Sirisena presided over the oath-taking ceremony.

"UNP Leader Ranil Wickremesinghe has sworn in as the Prime Minister before President Maithripala Sirisena a short while ago at the Presidential Secretariat," reported Sri Lanka's Daily Mirror.

Mahinda Rajapaksa on Saturday resigned from the post of Sri Lankan PM.

Rajapaksa was appointed as prime minister by President Maithripala Sirisena on Oct 26.

Maithripala Sirisena in October sacked Prime Minister Ranil Wickremesinghe and appointed former president Mahinda Rajapaksa as the new premier. 

Relations between Sirisena and Wickremesinghe's political parties, who have governed in coalition since 2015, received setback since both suffered humiliating losses in February's local council elections.

Image: Harsha De Silva Twitter page