The announcement by Maithripala Sirisena on November 21 came as a blow to President Mahinda Rajapaksa, who had declared the previous day that he would seek an unprecedented third term as president and called a snap election. The vote is scheduled to take place in early January.
Talking to reporters at a press conference, Sirisena said "one family has taken control of the economy, power and the party. The country is moving towards a dictatorship."
The former minister, who previously also held the position of general secretary of Rajapaksa's Sri Lanka Freedom Party (SLFP), has been backed by the main opposition party the United National Party (UNP), as well as many of Rajapaksa's rivals.
Although the president still has wide public support, internal tensions within the ruling party have seen backing for his leadership decline.
There have also been allegations President Rajapaksa has used his position to give friends and family members jobs in high-ranking government and bureaucratic institutions.
Nira Wickramasinghe, South Asia expert at Leiden University in the Netherlands, says in a DW interview that Rajapaksa's decision to call a snap election comes at a time when his support base is getting dangerously low. She says Sirisena has a strong support base backing him in his bid to become leader.
DW: What are the reasons behind Maithripala Sirisena's decision to challenge President Rajapaksa?
Nira Wickramasinghe: Maithripala Sirisena was nominated by a united group of opposition parties to carry out a specific program. His main aim is to abolish the executive presidency in 100 days and pave the way for a return to a parliamentary democracy. In addition, he has pledged to restore the 17th amendment [making the police, elections, public service and the judicial service commissions fully independent] and repeal the 18th amendment [changes in term limits for re-elections of the president].
Sirisena also intends to hand over the post of prime minister to the current leader of the opposition, Ranil Wickremesinghe, if he were to win the election - a promise that he will need to explain to his electorate. His decision to challenge President Rajapaksa has weakened the present government.
How might Sirisena's background affect the snap elections in January?
He served as health minister in the current president's cabinet before he quit to challenge Rajapaksa. He has long had prime ministerial ambitions. He was also general secretary of Rajapaksa's Sri Lanka Freedom Party.
Sirisena is a seasoned politician who can rally votes from the Sinhalese rural heartlands where the president has long been uncontested. Unlike many other politicians, his name is not associated with corruption scandals, or other misdemeanors. Neither is he seen as hostile to minority groups.
Why do you think President Rajapaksa called for elections now?
Rajapaksa saw that his voter support was eroding. The last provincial elections in Uva showed a big drop in his popularity, and even the support for his coalition dropped around 20 percent. Though the opposition didn't win in the provincial elections, they scored higher than they ever had before - which showed a dramatic change in opinion among voters.
So it was a strategic move by the president to hold elections two years early, in an effort to stem the flow of voters moving towards other parties.
Do you think the recent announcement by Sirisena made Rajapaksa regret his decision?
The opposition was probably waiting for Rajapaksa to declare that he was holding elections before they made their own move. The president will muster all his energy and resources to defeat his rival. It will not be an easy contest for Sirisena.
How have Sri Lankans reacted to the news of Sirisena's candidacy?
Among those who want change, it is predominately positive. With the news that Sirisena will now contest the presidency, there seems to be some hope that at least now there will be a serious contest.
Sirisena has received strong endorsement from both opposition leaders as well as members of the ruling SLFP who are dissatisfied with Rajapaksa’s governance style. Even former President Chandrika Kumaratunga has declared her support for Sirisena, although it may signal a possible return of the Bandaranaike dynasty. Sirisena has also recently been backed by prominent monk and former potential candidate, Ven. Maduluwawe Sobitha Thero. As always in Sri Lanka, there will be plenty of crossovers as the tide appears to turn.
It will be interesting to see what issues will come to the fore in the campaign. Sirisena has promised to refrain from personal attacks. But will this be possible against a regime founded on nepotism and thriving on patronage networks? There is a strong case against a regime that has kept economic and political capital in the hands of a ruling clique. I wonder whether Sirisena will be able to recapture a democratic political space from dynastic rulers of the present and the past.
Nira Wickramasinghe is a professor of Modern South Asian Studies at the Netherlands' Leiden University.