Kim, 58, who served as World Bank president for more than six years, says he plans to join a firm that will focus on increasing infrastructure investments in developing countries.
"It has been a great honor to serve as President of this institution, and I want to thank all of you for your support to our mission of ending poverty in the world", Kim wrote to World Bank staff in an email Monday morning.
World Bank chief executive officer Kristalina Georgieva will assume the role of interim president.
Under Kim, the bank set the goal of eliminating extreme poverty by 2030 and ramped up financing to developing countries.
David Malpass, the Treasury's undersecretary for worldwide affairs, has questioned the need for additional resources for the World Bank and other global financial institutions, arguing instead that the lenders should focus more of their resources on poorer countries and lend less to middle-income countries such as China.
Kim, the former head of Dartmouth College, was first tapped by former President Barack Obama to lead the World Bank in 2012.
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Some paused outside the headquarters of Agence France-Presse ( AFP ) in central Paris to hurl anti-media insults. Cops used clubs to thwart protestors who tried to cross a bridge off the sanctioned marching route.
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.
Kim cultivated close relations with Trump's daughter Ivanka, who works as a White House adviser.
Dr Kim was nominated to the post for two terms by former U.S. president Barack Obama, and advocated financing for green energy projects while dropping support for coal power investments.
The Trump administration has put pressure on the World Bank to justify its lending practices, including loans to China.
Treasury Secretary Steven Mnuchin looks forward to working with other countries on the bank's 24-member executive board to select Kim's successor, a Mnuchin spokesperson said.
But Paul Cadario, a former World Bank senior manager now at the University of Toronto's Munk School, noted that the Trump administration had not named a representative to the bank's board of directors - meaning the question was likely not high on the administration's radar.