Jayaratne said Rajapaksa will be able to contest for a third term in office as a result of the constitutional changes brought in by the government through the parliament, Xinhua reported.
The prime minister Tuesday confirmed that presidential election would be held January next year.
The opposition, on the other hand, said that the incumbent president can only contest for two terms.
However, Jayaratne said there is enough legal backing to allow the president to contest for a third term despite arguments raised to the contrary by the opposition, some lawyers and monks.
Rajapaksa said he and his government would contest for a third term in office and win comfortably.
The prime minister dismissed allegations that the president was taking decisions on his own on national issues.
He insisted that Rajapaksa sought cabinet approval on most decisions while parliament approval was also sought on issues when needed.