Once the most stable economy in Latin America, Chile has one of the world’s largest income gaps, with one percent of the population owning 25% of the country’s wealth, according to the United Nations.
Mr Boric has promised to address this inequality by reforming Chile’s pension and healthcare systems, reducing the work week from 45 to 40 hours, and boosting green investment.
His rival, meanwhile, stood on a platform of law and order, pledging cuts to tax and social spending.
Mr Kast also defended the legacy of former military dictator General Augusto Pinochet, who took power in a coup and ruled the country from 1973 to 1990. Under his leadership more than 3,000 people were murdered by the state or disappeared, and thousands of political opponents were held in internment camps.
In a tweet, Mr Kast said he had called Mr Boric to congratulate him on his “great triumph”.
“From today he is the elected President of Chile and deserves all our respect and constructive collaboration,” he added.
The country is going through huge changes after voting overwhelmingly last year to re-write Chile’s Pinochet-era constitution.
Mr Piñera said that Chile was living in “an environment of excessive polarization, confrontation [and] disputes,” and urged his successor to “be the president of all Chileans.”