He finished more than 12 points ahead of former guerrilla Gustavo Petro, though the runner-up's performance at the ballot box was the best ever for the left in one of Latin America's most conservative nations. He also promised a frontal attack on corruption while addressing a surge in cocaine production that he called a threat to national security.
The election was the first since outgoing President Juan Manuel Santos signed the peace agreement with the Revolutionary Armed Forces of Colombia and the race ultimately ended up being defined by the divisive accord.
Mr Duque's promise to heal the scars from five decades of bloody conflict will demand a quick response. The FARC rebels who demobilized under the accord are struggling to reinsert themselves into civilian life in a nation where many people are hesitant to forgive. Vast swaths of remote territory remain under the control of violent drug mafias and residual rebel bands. Mr Duque, who only entered politics in after being lured back to Colombia by former President Alvaro Uribe from a cosy life in Washington, in his victory speech repeated pledges made on the campaign trail to roll back benefits in the peace accord for top rebel commanders behind atrocities.
Mr Petro took his loss in stride, refusing to call it a defeat. He also promised to mobilise his considerable following into a combative opposition that will fight for social reforms and defend the peace accord. Colombia's peace process to end a conflict that caused more than , deaths is considered largely irreversible. Most of the more than 7, rebels who have surrendered their weapons have started new lives as farmers, community leaders and journalists.
Last year the rebels launched a new political party and will soon occupy 10 seats in congress. But the accord remains contentious and Mr Duque pledged throughout his campaign to make changes that would deliver "peace with justice". Through constitutional reform or by decree, he could proceed with proposals such as not allowing ex-combatants behind grave human rights abuses to take political office until they have confessed their war crimes and compensated victims.
