Former Sri Lankan defense minister Gutabaya Rajapagsa has won more than 52 percent of the vote, compared to 42 percent for government candidate Sagit Premadasa, who acknowledged his defeat in Saturday's election.
The president-elect announced his intention to be sworn in on Monday in the southern city of Anurad Habura, a Buddhist holy city, in reference to his electoral platform in which he adopted the rule of Buddhist Sinhalese culture in the country.
Rajapagsa, 70, launched a national campaign focusing on security after the April 21 attacks that killed 269 people on the South Asian island.
Rajapagsa's family is popular with Sri Lanka's majority Sinhalese after it defeated separatist Tamil Tiger rebels and turned the page in 2009 into a 37-year civil war.
Some Muslims, who make up 10 percent of the population, are worried about Gotabaya, especially after Muslims faced mass attacks in the aftermath of the attacks.