Moon Jae-in has been critical of the two previous conservative administrations, which took a hard-line stance against Pyongyang, for failing to stop North Korea’s weapons development.
Since the Korean War ended in an armistice in 1953, there have only been two summits where the leaders of the two Koreas have met, both held in Pyongyang.
Moon Jae-in spearheaded preparations for the second meeting in 2007, when serving as a presidential aide.
The US, South Korea’s most important ally, has congratulated Moon Jae-in on his victory.
White House press secretary Sean Spicer said the US looked forward to continuing to “strengthen the alliance” and “deepen the enduring friendship and partnership”.
Japan’s PM Shinzo Abe said their countries faced common challenges “led by responses to the North Korean issue” but they could “further contribute to peace and prosperity of the region by working together”.
China’s President Xi Jinping said he “always attaches great importance to the relationship between China and South Korea”, and that he was “willing to diligently work with” with Moon Jae-in to ensure both countries benefit, reported Chinese state news agency Xinhua.
A record turnout is predicted, with numbers boosted by younger voters, as South Koreans choose from 13 candidates.
Polls close at 20:00 local time, with the winner expected to be announced soon after. The new leader is likely to be sworn-in on May 10.
Heightened tensions on the Korean peninsula in recent weeks have made the perennial worries over the South’s volatile neighbor a key issue.
Moon Jae-in, of the Democratic Party of Korea, has advocated greater dialogue with North Korea while maintaining pressure and sanctions.
Both Moon Jae-in and Ahn Cheol-soo have urged President Donald Trump to cool his rhetoric towards North Korea after his administration suggested it could take military action over Pyongyang’s nuclear program.
However, Hong Joon-pyo of the conservative governing Liberty Korea Party has attacked Moon Jae-in’s approach, saying last week that the election was a “war of regime choices”.
North Korea state media said it favored a return to an earlier era of communication and co-operation known as the Sunshine policy, seen as an endorsement of Moon Jae-in who was part of the previous South Korean government which promoted that policy.
All the candidates are promising to protect the fragile recovery in the country’s economy – the fourth largest in Asia – and to bring down youth unemployment, which remains stubbornly high.
There have been vows to reform the family-run conglomerates – chaebols – which dominate the domestic economy.
Whoever wins will have to tackle ties with China, which retaliated economically over the deployment of a US missile defense system in South Korea.
Park Geun-hye had “concealed completely Choi Soon-sil’s meddling in state affairs and denied it whenever suspicions over the act emerged and even criticized those who raised the suspicions,” it said.
However, the judges dismissed some charges, including accusations Park Geun-hye had infringed on freedom of the press by creating a media blacklist of cultural figures, and criticism of her response during the 2014 Sewol ferry disaster.
North Korea announces it has carried out a live-fire artillery drill simulating an attack on the official residence of South Korean President Park Geun-hye, known as the Blue House.
The exercise was overseen by Kim Jong-un, said the KCNA state news agency, who called on the military to be ready to “ruthlessly” destroy the government in South Korea.
It is the latest in a series of angry gestures by Pyongyang.
South Korean President Park Geun-hye has ordered the army to be on alert.
However, Park Geun-hye said on March 24 that “reckless provocations will only become a path to self-destruction for the North Korean regime”.
North Korea has been reacting after the UN imposed some of its toughest sanctions following its nuclear and long-range rocket tests.
Pyongyang has also been angered, as it is annually, by joint US-South Korean military exercises taking place south of the border.
Already known for vitriolic language, the KCNA report threatened to turn South Korea’s presidential residence into a “sea of flames and ashes”.
“Artillery shells flew like lightning and intensely and fiercely struck targets simulating Cheong Wa Dae and rebel governing bodies in Seoul,” it said of the latest drill, using the Korean name for the Blue House.
It was not clear when the drill was carried out, but the report warned of a “miserable end” for President Park Geun-hye.
The Blue House (Cheongwadae) was attacked by North Korean commandos in 1968.
The attempt to assassinate then-President Park Chung-hee was unsuccessful, but seven South Koreans and most of the 31 North Koreans attackers were killed.