He was accompanied by his sister Kim Yo Jong and Foreign Minister Ri Yong Ho.
Regardless, Trump seemed determined to keep his meeting with Kim low-key, dangling the possibility of a future summit in the USA if things go well this week.
Tuesday's summit will be the first between a North Korean leader and a sitting American president.
For decades, North Korea has been a pariah state, and now its latest hereditary leader is being treated as a world statesman.
It will certainly be an exciting day and I know that Kim Jong-un will work very hard to do something that has rarely been done before ... Before the announcement, U.S. Secretary of State Mike Pompeo seemed to hint that the outcome of the talks might not be what Trump has promised in the past.
But on the eve of the summit, the White House unexpectedly announced Trump would depart Singapore by Tuesday evening, meaning his time with Kim would be fairly brief. India, Pakistan and North Korea are not CTBT signatories. Trump had previously said the talks might extend beyond the first day.
The talks have been portrayed by Trump in recent days more as a get-to-know-you session.
It's a dramatic departure for Trump, who kicked off 2018 bragging that his nuclear button is "much bigger" than Kim's.
The clearest benchmarks about what the U.S.is seeking from the summit, however, have come from Pompeo rather than Trump.
Kim told Lee: "The entire world is watching the historic summit between the DPRK and the United States of America, and thanks to your honest efforts. we were able to complete the preparation for the historic summit".
He's also repeatedly expressed his support for a meeting between Trump and Kim - even offering to facilitate it or serve as an ambassador of sorts.
The country's youth unemployment rate stood at 10.7 percent in April and job-seeker Kim Tae-young - who has a bachelor's degree in engineering and new materials - said: "Frankly speaking, I have no particular feelings about the summit, but I just hope it would help ease uncertainties".
Kim, on the other hand, has shown he is prepared for his moment on the world stage, and could end up outfoxing Trump, said Victor Cha, a senior adviser and Korea Chair at the Center for Strategic and International Studies in Washington.