South Korea's President-elect, Park Geun-hye, has said her victory will help the country's economy recover.
Ms Park, the daughter of former dictator Park Chung-hee, defeated her liberal rival Moon Jae-in. She will be South Korea's first female leader.
Votes are still being counted, but Mr Moon has admitted defeat. Turnout was high in a poll dominated by economic and social welfare issues.
Ms Park, 60, will replace her party colleague Lee Myung-bak.
He is stepping down as the law requires after his five-year term.
Combined figures from the networks released after polls closed gave Ms Park 50.1% of the vote over Mr Moon's 48.9%.
"This is a victory brought by the people's hope for overcoming crisis and economic recovery," she told supporters in the capital Seoul.
Economic growth has fallen to about 2% after several decades in which it averaged 5.5%.
With the country having split almost equally along party lines, the BBC's Seoul correspondent Lucy Williamson says Ms Park will have to work hard to improve relations with her detractors.
From the moment polls opened at 06:00 on Wednesday (21:00 GMT on Tuesday), millions of South Koreans queued to cast their ballots despite freezing temperatures.
Ms Park's supporters, wearing red party scarves, cheered as poll figures emerged.
Both bolstered and dogged by the legacy of her father, who built South Korea's economy while crushing dissent, she apologised in September for human rights abuses under his administration.
Mr Moon of the Democratic United Party is a former human rights lawyer who served under former President Roh Moo-hyun. He was briefly jailed by Ms Park's father in the 1970s.
Both candidates put forward broadly similar policies, promising to boost social welfare spending, close the gap between the rich and poor and rein in the family-run giant conglomerates known as chaebol.
The issue of North Korea did not feature heavily in the campaign despite its recent rocket launch.
Both candidates promised more engagement with Pyongyang - though in Ms Park's case, more cautiously than her rival.
Ties between the two Koreas deteriorated during Mr Lee's term.