Park Geun-hye is the daughter of a divisive military strongman from South Korea's authoritarian era. After five years under unpopular incumbent Lee Myung-bak, Park has vowed to engage with the North and send more aid, despite Pyongyang's widely condemned long-range rocket launch last week.
Some hope the landmark win could set the stage for talks with North Korea.
Both Park and her rival, liberal candidate Moon Jae-in, campaigned against the current administration's hard-line stance on North Korea. Moon is the son of North Korean refugees.
However, North Korean state media have condemned the sincerity of Park's North Korea police since she and Lee are from the same conservative party.
Many voters believe Lee's policies drove North Korea to renew nuclear missile tests and launch attacks in 2010 that killed 50 Koreans.
Huge crowds lined up in frigid weather throughout the day to choose between Park and Moon. Turnout was the highest in 15 years, and some analysts thought that might lift Moon, who is more popular with younger voters. Despite moving to the center, however, Park was carried by her conservative base of mainly older voters.
Park has created an image as a selfless daughter of Korea, never married, then a female lawmaker in a male-dominated political world.
After Moon conceded defeat, Park said that she would dedicate herself to uniting her people and improving their livelihoods.
"I really thank you. This election is the people's victory," Park told a crowd packing a Seoul plaza.
The Associated Press contributed to this report.