The 60-year old conservative, Park Geun-hye, will return to the presidential palace in Seoul where she served as her father's first lady in the 1970s, after her mother was assassinated by a North Korean-backed gunman.
With more than 88 percent of the votes counted, Park led with 51.6 percent to 48 percent for her left-wing challenger, human rights lawyer Moon Jae-in, giving her an unassailable lead that forced Moon to concede.
Her raucous, jubilant supporters braved sub-zero temperatures to chant her name and wave South Korean flags outside her house. When she reached her party headquarters, Park was greeted with shouts of "president".
An elated Park reached into the crowd to grasp hands of supporters wearing red scarves, her party's colour.
"This is a victory brought by the people's hope for overcoming crisis and for economic recovery," she told supporters at a rally in central Seoul.
Park will take office for a mandatory single, five-year term in February and will face an immediate challenge from a hostile North Korea and have to deal with an economy in which annual growth rates have fallen to about 2 percent from an average of 5.5 percent in its decades of hyper-charged growth.
She is unmarried and has no children, saying that her life will be devoted to her country.
The legacy of her father, Park Chung-hee, who ruled for 18 years and transformed the country from the ruins of the 1950-53 Korean War into an industrial power-house, still divides Koreans.
For many conservatives, he is South Korea's greatest president and the election of his daughter would vindicate his rule. His opponents dub him a "dictator" who trampled on human rights and stifled dissent.
"I trust her. She will save our country," said Park Hye-sook, 67, who voted in an affluent Seoul district, earlier in the day.
"Her father ... rescued the country," said the housewife and grandmother, who is no relation to the candidate.
For younger people, the main concern is the economy and the creation of well-paid jobs in a country where income inequalities have grown in recent years.
"Now a McDonald's hamburger is over 5,000 Korean won ($4.66) so you can't buy a McDonald's burger with your hourly pay. Life is hard already for our two-member family but if there were kids, it would be much tougher," said Cho Hae-ran, 41, who is married and works at a trading company.
Park has spent 15 years in politics as a leading legislator in the ruling Saenuri party, although her policies are sketchy.
She has a "Happiness Promotion Committee" and her campaign was launched as a "National Happiness Campaign", a slogan she has since changed to "A Prepared Woman President".
She has cited former British Prime Minister Margaret Thatcher, a tough proponent of free markets, as her role model as well as Angela Merkel, the conservative German chancellor who is Europe's most powerful leader.
NEGOTIATE WITH NORTH
One of those who voted on Wednesday was Shin Dong-hyuk, a defector from North Korea who is the only person known to have escaped from a slave labour camp there.
He Tweeted that he was voting "for the first time in my life", although he didn't say for whom.
Park has said she would negotiate with Kim Jong-un, the youthful leader of North Korea who recently celebrated a year in office, but wants the South's isolated and impoverished neighbour to give up its nuclear weapons programme as a precondition for aid, something Pyongyang has refused to do.
The two Koreas remain technically at war after an armistice ended their conflict. Kim Il Sung, the grandfather of the North's current leader, ordered several assassination attempts on Park's father, one of which resulted in her mother being shot to death in 1974.
Park herself met Kim Jong-un's father, the late leader Kim Jong-il, and declared he was "comfortable to talk to" and he seemed to be someone "who would keep his word".
The North successfully launched a long-range rocket last week in what critics said was a test of technology for an intercontinental ballistic missile and has recently stepped up its attacks on Park, describing her as holding a "grudge" and seeking "confrontation", code for war.
Park remains a firm supporter of a trade pact with the United States that and looks set to continue the free-market policies of her predecessor, although she has said she would seek to spread wealth more evenly.
The biggest of all the chaebol, Samsung Group, which produces the world's top selling smartphone as well as televisions, computer chips and ships, has sales equivalent to about a fifth of South Korea's national output.