The right-wing Abelardo de la Espriella, an admirer of Donald Trump, came top in the vote, followed closely by the left-wing senator Iván Cepeda, an ally of the current president Gustavo Petro.
The campaign was plagued with violence, including drone strikes, kidnappings, homicides and the assassination of a presidential candidate at a rally last year.
Both men offer differing visions for how to solve Colombia’s violent internal armed conflict that has lasted for decades but has resurged in recent years.
On Sunday, neither candidate achieved more than 50% of the vote to win outright.
While polls tipped Cepeda to finish ahead of his right-wing challenger, official results showed that he trailed, with 41% of votes compared to De La Espriella’s 43.7%, with almost all ballots counted.
