South Korea has elected liberal Lee Jae-myung as president to lead the country through a tumultuous period that will require negotiating trade tariffs with the U.S. and mending the scars from his ousted predecessor's shock martial law declaration.

Lee Jae-myung was sworn in as South Korea's president on Wednesday, just hours after his victory was certified in a snap election that brought an end to months of political turmoil in the country.

Mr. Lee cruised to victory on Tuesday after his predecessor pitched the country into chaos with a brief declaration of martial law.