Sri Lanka's prime minister Ranil Wickremesinghe resigned, bringing his government to an end following his party's presidential election debacle.

Ranil Wickremesinghe's move clears the way for new President Gotabaya Rajapaksa, elected on Saturday in a landslide, to appoint a replacement of his choice and a new government.

"The prime minister will have a final meeting with his cabinet as well as other leaders of his coalition before addressing the nation to announce his resignation," the official said on condition of anonymity.

Wickremesinghe's party put forward Sajith Premadasa in the presidential election but was soundly beaten by Rajapaksa in a highly divisive election in the island nation of 21.6 million.

He and brother Mahinda Rajapaksa are adored by the Sinhala-Buddhist majority -- but loathed among minority Tamils -- for spearheading the brutal crushing of Tamil Tiger separatists 10 years ago to end Sri Lanka's civil war.

Around 40,000 Tamil civilians were allegedly killed by the military in the closing stages of the conflict when Gotabaya Rajapaksa effectively ran the security forces and his brother was president.

During the three-month election campaign held in the shadow of Islamist extremist attacks in April, Rajapaksa had promised to make his charismatic and popular brother Mahinda his prime minister.