Gotabaya Rajapaksa, credited with defeating Tamil rebels and accused of war crimes, is considered a polarising figure.
Climate of fear prevails over the island nation a day after the worst attacks in a decade kill 290 people.
Rifts remain after deadly anti-Muslim riots in 2014 killed four and caused tens of thousands of dollars in damage.
Victims in Aranayake still in shock a week after massive mudslides killed more than 100 people with another 100 missing.
The former president will contest Monday’s poll for a seat in Sri Lanka’s parliament.
New Sri Lankan officials say domestic investigation is on the table, but international inquiry out of the question.
Brazen election bid by prominent defector may not end in victory, but it has shaken the nation’s political foundation.