Parties to the International Criminal Court (ICC) on Friday elected Britain’s Karim Khan as the new prosecutor for a nine-year term starting on June 16.

Khan won a secret ballot against three other candidates to replace lead prosecutor Fatou Bensouda. The 123-member Hague-based court, which began work nearly 20 years ago, handles war crimes, crimes against humanity, genocide and crimes of aggression.

British barrister Karim is best known for heading the United Nations’ special investigative team looking into Islamic State crimes in Iraq...