"The North's long-range missile launch symbolically showed how grave our security reality is," Park said following a visit to Seoul's National Cemetery, where she paid silent tributes to late presidents, including her father.
North Korean state media, however, have repeatedly questioned the sincerity of Park's North Korea engagement policy, since she and Lee are from the same conservative party.
Ties between the Koreas plummeted during Lee's term. Many voters believe Lee's policies drove North Korea to renew nuclear and missile tests and to launch two attacks in 2010 that killed 50 Koreans.
The rocket launch, which Park's party has called a test of banned ballistic missile technology, made North Korea an issue in the closing days of campaigning, although many voters said they cared more about the economy.
Park (Bahk guhn-hae) has said she is open to dialogue with North Korea, but she has also called on Pyongyang to show progress in nuclear dismantlement. She has also raised the possibility of a meeting with North Korean leader Kim Jong Un, but only if it's "an honest dialogue on issues of mutual concern."
Huge crowds lined up in frigid weather throughout the day to choose between Park and liberal candidate Moon Jae-in (Moon Jay-in), the son of North Korean refugees. Both candidates steered away from Lee's policies, including, most strikingly, his hard-line stance on North Korea.
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.
They fondly remember her father, Park Chung-hee, dictator for 18 years until his intelligence chief killed him during a drinking party in 1979.
Much of 60-year-old Park's public persona is built on her close association with her father's rule. When she was 22 her mother died in a botched attempt to assassinate her father, and she stood in as first lady for five years until her father's death.
She 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.
With about 98 percent of votes counted, Park had won 51.6 percent to Moon's 47.9 percent, according to the state-run National Election Commission. Park is to take office in February when Lee ends his single five-year term.
No Korean woman is believed to have ruled since the ninth century. Park becomes the most powerful figure in a country where many women earn less than men and are trapped in low-paying jobs despite first-class educations.
Her father's legacy is both an asset and a weak spot. Older South Koreans may revere his austere economic policies and tough line against North Korea, but he's also remembered with loathing for his treatment of opponents, including claims of torture and summary executions.
Park's win means that South Korean voters believe she would evoke her father's strong charisma as president and settle the country's economic and security woes, according to Chung Jin-young, a political scientist at Kyung Hee University in South Korea.
"Park is good-hearted, calm and trustworthy," 50-year-old housewife Lee Hye-Young said at a polling station at a Seoul elementary school. "Also, I think Park would handle North Korea better. Moon would want to make too many concessions to North Korea."