The National Election Commission said Park secured the votes to become South Korea's first female president by defeating Moon Jae-in, the candidate of the main opposition Democratic United Party.
With more than 99.3 percent of the vote counted as of 2:30 a.m., Park had 51.6 percent against Moon's 48 percent. The gap exceeded 1 million ballots.
The difference between the two exceeded predictions by a joint exit poll by the nation's three major broadcasters. The poll forecast that the 60-year-old Park would emerge as the winner with 50.1 percent of the vote against Moon's 48.9 percent, a gap of just 1.2 percentage points.
Her victory marks the first time that a candidate has won more than 50 percent of the vote since South Koreans started directly electing their chief executive in 1987.
She is also the first daughter of a former president to win the nation's top office.
Her father, President Park Chung-hee, took power in a military coup in 1961 and ruled the country for 18 years until his assassination in 1979. The president-elect served as acting first lady to her father for five years after her mother, Yook Young-su, was gunned down by an assassin.
Park's election also means conservatives will hold onto power for five more years, which could affect South Korea's economy, foreign policy, its stance against North Korea and political and social reforms.
In a ceremony to mark her victory in downtown Seoul, Park pledged to follow through on her campaign promises.
"I will become a president of the people's livelihoods who keeps her promises to the people and open an era in which the people are happy," Park told a rally of supporters.
"This election was a victory for you, the people," she said. "I promised three main things during my campaign: to become a president of the people's livelihoods, a president who keeps promises, and a president who achieves grand unity."
Park, who turns 61 in February, has built a reputation as a politician who values principle and trust, and this view seems to have appealed to voters.
After winning her parliamentary seat five times in a row, and leading the Saenuri Party through numerous crises as party chairwoman or interim leader, Park has won the nickname "queen of elections" for turning expected defeat in the polls into victory.
With Park's victory confirmed, the Saenuri Party said that it will pool all of its resources to meet the expectations of the people, such as pushing forward economic democracy and job creation for the young, and will strive to restore trust in politics among the people.
Moon conceded defeat late Wednesday after polls showed that he was hopelessly behind.
At a press conference at his party office, the 59-year-old human rights lawyer and former chief of staff to the late President Roh Moo-hyun said he did his best.
"I was unable to bring about a change in government and meet the people's call for the start of new politics," he said. "I hope that Park will strive for national unity and co-prosperity and lead the country well in the future."