A bilateral meeting at the White House between a U.S. vice president and a visiting head of state – followed by a joint appearance featuring the two – is highly unusual.
The event included a photo-op of Harris and Moon walking and talking before the meeting, which included Moon and several of his aides, and Harris and several of hers.
Harris’ session with Moon was not the first time the vice president has spoken on her own with a world leader.
Harris also took a call with Jordanian King Abdullah II on Thursday, to address the Israeli-Palestinian cease-fire in Gaza.
Since taking office in January, Harris has also spoken with French President Emanuel Macron, Canadian Prime Minister Justin Trudeau and Israeli Prime Minister Benjamin Netanyahu.
In April, Harris also welcomed Japanese Prime Minister Yoshihide Suga to the White House before the Japanese leader met later with Biden.
Fox News could not immediately reach the White House for comment on what she and Moon discussed, but Harris said that "challenges that exist on the Korean peninsula" would be at the top of the list.
She later posted a Twitter message about the meeting.
"Today, I met with Republic of Korea President Moon," she wrote. "We discussed North Korea, global health, and how we can address the root causes of migration from the Northern Triangle. We look forward to working with President Moon to address the challenges we face."
The vice president pledged in other remarks to work with South Korea to promote "a region that is unconstrained by coercion."
Harris’ vice presidency has played a significant part in building up U.S. foreign relations – an issue that was at the cornerstone of Biden’s presidential campaign.
She has also been tasked with addressing the "root causes" contributing to the crisis at the southern border, which has meant strengthening U.S. ties with Mexico, El Salvador, Honduras and Guatemala.
Harris will take her first international trip in June to Mexico and Guatemala in an attempt to stop the endless stream of migrants arriving at the southern border.
Fox News' Brie Stimson contributed to this report.