After practicing law for several years with the firm Milbank, Tweed & Hope, King became one of the United States prosecutors at the Nuremberg Trials, serving from 1946 to 1947.
Efter at have været advokat i flere år i firmaet Milbank, Tweed & Hope blev King en af De Forenede Staters anklagere ved Nürnbergprocessen i 1946-1947.