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Moon was elected on the back of anti-corruption protests which helped turf out his predecessor Park Geun-hye, now facing criminal charges, and his promise of sweeping reforms to the country's political system, economy, and chaebols, the family run conglomerates, that dominate South Korean society.
But while he has made progress on those points, his biggest success -- or failure -- may come in dealing with Pyongyang.
"No South Korean president in recent years has had to focus quite so much on the country's noisy neighbor," said Oliver Hotham, managing editor at the Seoul-based Korea Risk Group.
"Moon has also faced the most unpredictable and erratic US leader in decades, and has had to, in many ways, pick up a lot of diplomatic slack on the issue."
New Sunshine Policy?
But now comes the real test.
During his presidential campaign, Moon's approach was compared to the "Sunshine Policy" pursued by Presidents Kim Dae-jung and Roh Moo-hyun, but in practice it has proven different.
Under the "Sunshine Policy" -- for which Kim won the Nobel Peace Prize in 2000 -- Seoul actively engaged Pyongyang economically and diplomatically, and provided considerable humanitarian aid.
However, the approach did not secure any concrete gains, and it struggled to gel with a more aggressive US administration under President George W Bush, who labeled North Korea part of the "axis of evil" in 2002. The following year, Pyongyang withdrew from the Nuclear Nonproliferation Treaty and began pursuing atomic weapons in earnest.
While Moon has been consistently pro-engagement, he has also supported US President Donald Trump's tough line on North Korea's nuclear and weapons testing, which has included stringent economic sanctions and threats of military retaliation.
Moon approved the controversial deployment of a US missile defense system last year, over protests from locals and objections of many of his supporters on the left, who saw it as a needless provocation.
"Moon is maintaining close coordination with the United States, and is looking for small concrete steps to take to ease tensions, but does not expect to simply change the North's behavior through engagement," said Rodger Baker, VP of strategic analysis at global intelligence firm Stratfor.
"(His) desire is to reduce the sense of imminent war in return for engagement, a much more modest goal."
Domestic support
Hotham, the Korea Risk Group expert, said Moon has "staked a lot on his more diplomatic approach to the North working."
"So far it has, but if it all falls apart and we see renewed tension on the peninsula he'll be seriously damaged," he said.
However, Anwita Basu, an analyst at the Economist Intelligence Unit, said most South Koreans have such low expectations of progress with the North that short of starting a war "his credibility does not wrest on the outcome of the talks."
"Moon will return with battle scars and remain the president who made efforts to tame the belligerent neighbor," she said.
Stratfor's Baker agreed that Moon should not face significant blowback if the talks fall apart, but pointed out opposition parties are already "highly critical" of the summit, and will certainly seek to capitalize on any failure.
While a collapse in talks might not hurt Moon in the long run, an embarrassing failure it could derail his plans, particularly if his Democratic Party suffers in gubernatorial and local elections later this year.