The candidates including former defence secretary Gotabaya Rajapksa, minister Sajith Premadasa and former army chief Mahesh Senanayake filed their nominations before the elections commission Monday morning.
A total of 41 candidates had submitted security deposits but six did not file their nominations.
The main contest will be between Gotabaya Rajapaksa, brother of former President Mahinda Rajapaksa and Sajith Premadasa, son of late President R. Premadasa.
This is the first time that neither sitting President nor the leader of opposition are contesting the elections.
President Maithripala Sirisena’s Sri Lanka Freedom party (SLFP) has not announced which side it will support.
Leader of opposition Mahinda Rajapksa is not eligible for elections and is leading Sri Lanka People’s party (SLPP) of whose Gotabaya is the candidate.
SLPP broke away from SLFP after Sirisena emerged victorious against Mahinda Rajapaksa in 2015 elections.
Sajith Premadasa represents the alliance of United National Party (UNP) led by Prime Minister Ranil Wickremsinghe.
National security and economic stability have emerges as key factors in the coming elections.