The United Nation's secretary-general from 1953 to 1961, Dag Hammarskjöld, whose spiritual beliefs influenced his political activity, was searching for universality and solidarity as written in the charter of the UN. While in office, Hammarskjöld was able to unite personal belief and political rationale. This is the main reason he became a respected and true international civil servant. Hammarskjöld was neither a pure idealist nor a pure realist. This article examines the moral but not moralistic life and legacy of Hammarskjöld, who united mystics and realistic political engagement. In doing so it draws on the lessons learned from a “practical mystical” and international civil servant. This is chiefly done by using the English School approach of international relations theory while at same time pointing out the impact of positive mimesis. By devoting his private life to God, Hammarskjöld was able to devote his political life to the UN.