By Eliott C. McLaughlin and Amir Vera, CNN

(CNN) -- Ivan Duque is projected to win Colombia's presidency, according to Colombia's National Registry of Civil Status. More than 99% of votes have been counted.

Duque, a social conservative and member of the Democratic Center party, received almost 54% of the votes Sunday, while his opponent, former mayor of Bogota Gustavo Petro, got about 41% of the votes.

Current Colombian President Juan Manuel Santos said on Twitter on Sunday that he called Duque to congratulate him and "give him best wishes."

"I offered him total collaboration of the government to make an ordered and peaceful transition," the tweet read.

Duque, 41, served as a senator for four years and as an adviser to the Finance Ministry and the Inter-American Development Bank. He also is a professor and writer who co-authored the book "The Orange Economy."

Former President Alvaro Uribe said he voted for Duque "because they are a guarantee of growth and social inclusion ... that Colombia may not fall in the destructive socialism. I have voted with my soul wishing that the sun will shine on a new born democracy of our sister Venezuela."

Duque's projected victory comes after a May 27 presidential election when no candidate won 50% of the vote. At the time, initial results showed Duque led with 39% of votes. In second place was Petro with 25%, closely trailed by centrist Sergio Fajardo.

The election is seen by some observers as a referendum on the country's peace deal with FARC rebels.

Six candidates were vying to fill the seat left by departing President Santos, who was awarded the 2016 Nobel Peace Prize for his efforts to end the long-running civil war between his government and guerillas from FARC, or the Revolutionary Armed Forces of Colombia.

Under the deal, the rebels agreed to lay down their arms, exit the jungle and pursue their aims via politics rather than guerrilla warfare.

The front-runners in the election to replace Santos differed on the peace deal. Left-wing Petro supports the deal and blames former President Uribe for the turmoil wrought by FARC, while conservative Duque has taken tough stances against FARC and openly opposes the deal.

Other important issues include unemployment, health care and corruption.

Though there have been isolated incidents of violence related to the election, they have been minimal, likely owing to the dismantling of FARC and the Defense Ministry deploying 240,000 troops to ensure safety during the election process.

More than 36 million Colombians were eligible to vote in the election.