“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,” said Kim in a statement published by the World Bank's website on 7 January.
The Washington-based organisation is one of the most important donors to developing countries.
At times, its policies have been criticised and controversial, but it also has been credited with successful infrastructure projects across Asia, Africa and South America since its creation after the Second World War.
Kim's surprise early departure potentially hands US leader Donald Trump a key lever over development lenders with whom his administration has been at odds.
After reshaping the US presidency, traditional alliances, trade relations and the US Supreme Court, Trump now could have a chance to influence how countries like China access concessional lending.
But if Trump wants an American in the post, he will need to pick a candidate who can win the support of most shareholders, and will likely face many challengers.
As the biggest shareholder, the United States has sway over the selection of the new World Bank president, a post for 75 years always filled by an American, with the backing of European nations.