The swearing in ceremony was held inside the premises of the Presidential Secretariat at 9:30 am. President Sirisena administered the oath of office to 66-year-old Wickremesinghe, who has already served three times as the prime minister.
Prime Minister Narendra Modi on Monday night left for New Delhi after wrapping up his two-day visit in Paris during which he attended the crucial climate change conference.
"My heart goes out to the families of the victims and the injured," Modi said.
On a day of high political drama when the ruling coalition of Sri Lankan President Mahinda Rajapaksa suffered serious defections, the election commission on Friday set January 8, 2015 as the date for a snap presidential election.
Lanka is witnessing a political crisis since October 26 when President Sirisena sacked Wickeremesinghe and replaced him with Rajapaksa.
Sri Lanka's former World Cup-winning captain Arjuna Ranatunga says the administration of the game in the country is 'disgusting' and he has stopped following the national team for this reason.
President Maithripala Sirisena's government in Colombo has clearly decided to restore some balance in its diplomatic outreach, which presents a great opportunity for India.
India has dismissed reports that the Colombo station chief of the Research and Analysis Wing had been expelled in the run up to this month's Sri Lankan presidential election and maintained that he has moved out after completion of his three-year tenure.
'If there is a push towards a Marxist oriented government it will be dangerous.' 'We have seen this in Nepal and Myanmar and it will be a concern for India if it is surrounded by countries with such political dispensations.'
Dr Anil Jasinghe, Director General of the Health Services, said the larger death toll was released as a result of a calculation error.
Modi, who is on a two-day visit to Sri Lanka, made the announcement of the beginning of the flights during his address at the inauguration of the International Vesak Day, the biggest festival of Buddhists.
India invited leaders of the BIMSTEC countries as well as Kyrgyz President Jeenbekov, the current chair of the Shanghai Cooperation Organisation, and Mauritius PM Jugnauth for the Modi's swearing-in.
The dissidents, led by former president Sirisena's Sri Lanka Freedom Party, would leave the ruling Sri Lanka Podujana Peramuna coalition with its 14 Members of Parliament, party sources said after their meeting with the President on Monday.
PM Modi is due in Colombo on Friday.
Sri Lankan batting legend Kumar Sangakkara fought back tears in an emotional farewell where the country's President Maithripala Sirisena stumped him by offering the High Commissioner's post to United Kingdom, in Colombo, on Monday.
'Sirisena will keep both Rajapaksa and Wickremesinghe on tenterhooks till the next general election due in 2020,' says Aditi Phadnis.
Sri Lanka's former president Mahinda Rajapaksa on Tuesday accepted defeat in the parliamentary elections even before the announcement of the final results.
Incumbent Ranil Wickremesinghe is set to take oath as Sri Lanka's new prime minister of a unity government on Tuesday after his United National Party appeared close to a simple majority, with rival Mahinda Rajapaksa admitting defeat in the closely contested parliamentary polls.
Prime Minister Narendra Modi on Tuesday said India attaches "paramount importance" to strengthening relations with countries in the Indian Ocean region, which is vital for its security and progress.
Sri Lanka's new government on Sunday said it will probe whether longtime president Mahinda Rajapaksa sought military help to cling to power after he realised that he had lost the closely contested election.
Political analysts said Sirisena's move to install Rajapaksa as the prime minister could lead to a constitutional crisis as the 19th amendment to the Constitution would not allow the sacking of Wickremesinghe as the premier without a majority.
Sabka sath, sabka vikas, said Maldives President abdulla Yameen.
Over 15 million voters are eligible to vote in the election being held under electoral districts-based proportional representation system.
Ahead of Sri Lankan Prime Minister Ranil Wickremesinghe's first foreign visit to India, at least 16 Indian fishermen arrested recently for allegedly poaching in Sri Lankan waters will be released in a goodwill gesture.
Maithripala Sirisena is expected to meet his Indian counterpart Pranab Mukherjee besides holding talks with Prime Minister Narendra Modi
'The ban is to ensure national security... No one should obscure their faces to make identification difficult,' Sirisena's office said in a statement.
Ending months of speculation, Sri Lanka's vanquished former president Mahinda Rajapaksa on Wednesday announced his return to electoral politics, saying he will lead an opposition faction during the general elections in August.
Prime Minister Narendra Modi and Sri Lankan President Maithripala Sirisena on Monday held talks at Hyderabad House
Mahinda Rajapaksa has been accused by the Opposition of inciting the ruling party mobs to attack peaceful protesters by making a defiant speech while addressing several thousands of his supporters to deflect calls for his resignation.
Hundreds of Muslim women on Friday protested against the Sena mouthpiece.
Security has been beefed up in Sri Lanka as the army increased its deployment by 1,300 to 6,300.
Rajapaksa informed the lawmakers of United People's Freedom Alliance that he has resigned from the post.
The docking of two Chinese submarines at the Colombo harbour in 2014 had angered India, which said it undermined its security interests.
For India to view the new Sri Lankan leadership only through the prism of the past or through their narrow view on China, is fraught with possibilities that should be avoided, asserts N Sathiya Moorthy.
Dealing with the Sirisena government in Sri Lanka, says G Ganapathy Subramaniam, is a lot easier for India than engaging with the Rajapaksa regime.
The two brothers led a decisive campaign that helped end the island nation's three decade long civil war against the Liberation Tigers of Tamil Eelam.
In the aftermath of the Easter Sunday terrorist attacks, allegations have been made that the Muslim militants in Sri Lanka draw sustenance from India. An overarching impression is being created that the ISIS is gaining ground in India, points out Ambassador M K Bhadrakumar.
PM also invoked 'chai pe charcha', saying it was not just a slogan but a 'mark of deep respect for the dignity and integrity of honest labour'.
Pope Francis on Tuesday called for respect of human rights and healing of racial and religious hatred as he arrived on a two-day visit to Sri Lanka, days after a new government assumed power in the country.
India welcomed resolution of the political crisis in Sri Lanka and exuded confidence that relations between the two countries will continue to move on in an upward trajectory.