The new government has decided to restrict the size of the Cabinet to 26, though it can be increased up to 30 in terms of the 19th Amendment to the Constitution
Sri Lanka's existing parliamentary term ends next August, and the Constitution allows the president to dissolve the legislature in March and go for an election.
Mahinda won power in 2005 and went on to become South Asia's longest-serving leader. He became the country's youngest ever parliamentarian in 1970 at the age of 24
The counting will start soon after the end of voting. The first results are expected after mid night, officials said. The final results will come on Monday.
At stake is the stability of a nation that has increasing strategic importance due in part to its proximity to some of the world's most important sea lines
Sri Lanka has been gripped by constitutional turmoil since President Maithripala Sirisena sacked his former ally, prime minister Ranil Wickremesinghe, and his cabinet on October 26