“That peace we long for — that demands corrections — will have corrections, so that the victims are the centre of the process, to guarantee truth, justice and reparation”, Duque told supporters in his victory speech at his campaign headquarters.
“The time has come to build real change,” Duque said, promising a future for Colombians “of lawfulness, freedom of enterprise and equity,” after decades of conflict.
His vanquished opponent Petro promised to resist any fundamental changes to the deal.
His efforts to end the war with the Revolutionary Armed Forces of Colombia (FARC) brought him the Nobel Peace Prize, though he is leaving office with record unpopularity in a country of 49 million people.
The world’s leading producer of cocaine, the Latin American country continues to battle armed groups vying for control of lucrative narco-trafficking routes in areas FARC once dominated.
Duque’s victory means he will be Colombia’s youngest president since 1872.
Duque is buoyed by the backing of his popular mentor, former president and now senator Alvaro Uribe, whose two-term presidency from 2002-2010 was marked by all-out war on the FARC.
Petro, 58, was the first leftist to reach a presidential runoff in Colombia, and believed his presence showed the South American country had shed its suspicions of the left, tainted by 50 years of conflict.
“The need to change things is fundamental”, he said after voting.
Highlighting Colombia’s glaring inequalities during his campaign, Petro also said he would buy out land owned by the big agro-industrial companies and redistribute it to poor farmers.
Polls closed at 4:00 pm (2100 GMT) after a day of peaceful voting.
‘WE ARE IN LIMBO’
“The biggest challenge will be to adopt a clear position on the peace agreement because, for the moment, we are in limbo,” Fabian Acuna, professor of political science at Colombia’s Javeriana University, told AFP.
“It will be very costly to go backwards,” Acuna warned.
According to Andres Ortega of National University, Duque will “arrive with a very strong coalition in Congress”, where the right swept the polls in March legislative elections.
The FARC withdrew from the presidential elections, having suffered a drubbing in its first electoral contest as a political party in March, polling less than half a percent.
It still gets 10 seats in Congress as a result of the peace agreement — a clause Duque is intent on scrapping.