In an email to employees of the lender, Kim said he'll join a private firm focused on infrastructure investments in developing countries.
Announcing his decision on Monday, Kim said in a tweet: "It's been the greatest privilege I could have ever imagined to lead the dedicated staff of this great institution to bring us closer to a world that is finally free of poverty".
Kim was was re-elected for a five-year term in 2017.
Two people familiar with Mr Kim's announcement to the World Bank executive board said he was leaving of his own accord and was "not pushed out" by the Trump administration.
"The world is suspicious of the Trump administration, which has a different agenda for the bank", Sobel said in a phone interview.
Last year, it also won Trump administration support approval for a steep US$13 billion (RM53 billion) capital increase after acceding to Washington's requests to curb loans to higher-income countries like China.
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During the surprise meeting at Beijing's Great Hall of the People, Kim told Xi he was committed to giving up his nuclear arsenal. Coal exports to China fell to 4.83 million tonnes in 2017, from more than 20 million tonnes in 2016, according to Chinese data.
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It did not publicly name the winning candidate, but it is widely reported that the Catholic observers have identified Mr. Congo faces what could be its first democratic, peaceful transfer of power since independence from Belgium in 1960.
The World Bank committed almost $US64 billion in loans to developing countries in the fiscal year ended June 30 last year.
Trump's decision could affect how the bank deploys its capital at a time when emerging markets are facing growing stress from rising U.S. interest rates and trade tensions.
The rise of populism and the contentious debate over globalisation is raising the political pressure on leaders of organisations such as the World Bank, he said in an interview. He said details of his new position would be made public later.
The abrupt resignation could prompt a clash between the Trump administration and other governments over the future of the worldwide body.
The bank's board thanked Kim for his leadership and said in a statement it would "immediately" begin the process of looking for the next president.
Its sister lending agency, the International Monetary Fund, has always been headed by a European. In that race, Kim beat out Ngozi Okonjo-Iweala, then Nigeria's finance minister, and Jose Antonio Ocampo, a Colombian national and professor at Columbia University in NY.
In 1987, Dr Kim co-founded Partners In Health, a non-profit medical organisation that now works in poor communities on four continents. He was born in Seoul and grew up in Iowa.