Kim's departure will give President Donald Trump the opportunity to nominate his own choice to fill the World Bank post.
"It has been a great honour to serve as President of this remarkable institution, full of passionate individuals dedicated to the mission of ending extreme poverty in our lifetime", Kim said.
Mr Kim intends immediately to join a firm to focus on increasing infrastructure investment in developing countries, the bank said, without providing further details on the position.
According to the World Bank, Kim's leadership set two goals for the bank: "to end extreme poverty by 2030; and to boost shared prosperity, focusing on the bottom 40 percent of the population in developing countries".
Last April, the Bank also increased its capital by $13 billion with the unexpected support of the Trump administration.
As World Bank President since July 2012, the outgoing World Bank Group head noted infrastructure finance as one of the greatest needs in the developing world.
The World Bank says he will be succeeded February 1 on an interim basis by Cristalina Georgieva, its chief executive officer.
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World Bank President Jim Yong Kim speaks at the Milken Institute 21st Global Conference in Beverly Hills, California.
Kim's decision to quit for the private sector was described by sources close to the bank as a sudden and "personal decision" that surprised its shareholders - the 189 nations that support its work.
Its sister lending agency, the International Monetary Fund, has always been headed by a European.
Already the United States nominee was challenged for the first time in 2012 by two contenders.
World Bank staff also chafed at a widespread internal restructuring that Kim began, as well as spending and staff cuts.
A spokeswoman for the US Treasury, which oversees the US voting interest in the World Bank, said that Treasury Secretary Steven Mnuchin "looks forward to working with his fellow governors in selecting a new leader".
Those same developing countries have become "increasingly opposed to USA dominance over the global development bank", the report added.