Kast secured 59.16 per cent of the vote in a runoff with leftist candidate Jeannette Jara, on 40.84 per cent per cent, with over 57 per cent of ballots counted.
"Democracy has spoken loud and clear," Jara said as she conceded defeat.
"I have communicated with Jose Antonio Kast and wished him success for the good of Chile."
Kast has been a consistent hardliner throughout his decades-long political career. He has proposed building border walls, deploying the military to high-crime areas, and deporting all migrants in the country illegally.
His victory marks the latest win for a resurgent right wing in Latin America. He joins Ecuador's Daniel Noboa, El Salvador's Nayib Bukele, and Argentina's Javier Milei. In October, the election of centrist Rodrigo Paz ended almost two decades of socialist rule in Bolivia.
It was Kast's third run at the presidency and second runoff, after losing to leftist President Gabriel Boric in 2021. Once seen by many Chileans as too extreme, he has attracted voters who have become increasingly concerned by crime and immigration.
While Chile remains one of the safest countries in Latin America, violent crime has spiked in recent years as organised crime groups have taken root, capitalising on the country's porous northern desert borders with coca-producing neighbours Peru and Bolivia, major international marine ports, and surge of migrants susceptible to human and sex trafficking.
The vast majority of migrants in Chile illegally have arrived from Venezuela in recent years, government data shows.
Kast's proposals include creating a police force inspired by US Immigration Customs and Enforcement to rapidly detain and expel migrants in the country illegally.
He has also touted massive cuts in public spending.
However, Kast's more radical proposals are likely to face pushback from a divided Congress. While right-wing parties won seats in both legislative houses in a November general election, most of those gains came from more traditional parties. The Senate is evenly split between left and right-wing parties, while the swing vote in the lower house belongs to the populist People's Party.
Chile is the world's largest copper producer and a major producer of lithium and expectations of less regulation and market-friendly policies have already buoyed the local stock market, peso and equity benchmark.
Kast has previously been outspoken against abortion and the morning-after pill, but changing the country's abortion laws would require a majority in Congress to pass.
