Preliminary results from Sunday night showed Acción Ciudadana had garnered 77.8 percent of the votes compared to 22.15 percent for Liberación Nacional.
Still, nearly half of the country's registered voters abstained from filling out ballots, according to the Tribunal Supremo de Elecciones.
While the president elect again echoed the virtues of change he carried throughout his campaign, he said this was a historic moment of transition for Costa Rica.