LIMA, July 4 -- The daughter of Peru's most consequential and most divisive former leader declared her country ready for a "new stage" on Thursday, hours after electoral authorities formally handed her one of the narrowest presidential victories in recent Latin American history. Keiko Fujimori will be Peru's ninth president in ten years, the first to take office while her father remains in prison serving a twenty-five-year sentence for crimes against humanity.

Peru's National Elections Tribunal, known by its Spanish initials JNE, declared Fujimori the winner of the June 7 runoff on Thursday, with 50.135 percent of the vote against former Prime Minister Roberto Sanchez's 49.865 percent, a margin of roughly 50,000 votes out of more than 18...