The 66-year-old was picked by President Maithripala Sirisena, who handed a shock defeat to Mahinda Rajapaksa in January polls, to lead a minority government in January.
After winning the parliamentary polls this week, Wickremesinghe was today sworn-in as the Prime Minister for the fourth time in his political career spanning four decades during which he has held many important posts.
He has vowed to strengthen ties with India but has taken a tough stand on the fishermen issue as in March he stoked a controversy suggesting that Indian fishermen may be shot if they intruded into Sri Lankan waters.
He was also elected as the Prime Minister from 2001-2004 when the United National Front Government won the general elections in 2001. But he lost power in 2004, after Chandrika Kumaratunga called early elections.
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During his term as Prime Minister, he began peace talks with the LTTE, even offering a power-sharing deal.
Both Kumaratunga and Rajapaksa had accused him of being too lenient with LTTE and of offering them too many concessions.
When he assumed Prime Minister's office for the third time earlier this year, he pledged to devolve power to the country's Tamil minority, in a step towards national reconciliation six years after a military offensive crushed the LTTE.
"We will implement the 13th amendment within a unitary state," Wickremesinghe had said. The 13th amendment envisages the devolution of powers to the provinces.
Born in 1949 after Sri Lanka gained independence from the British, Wickremesinghe was elected to Parliament in 1977 at the age of 28, having worked in the Youth League of the United National Party (UNP) from his university days.
As the youngest minister in Sri Lanka at the time, he held the post of Deputy Minister of Foreign Affairs under President Jayewardene.