The victory in the most severe election since 1997 pledged that new President Lee Jae-myung would bring South Korea through the martial law crisis and economic recovery.
This is the day of judgment, Lee told thousands of people gathered outside the National Assembly on the evening of June 3, just hours after the poll showed him winning 49.42% of nearly 35 million votes, far ahead of conservative opponent Kim Moon-soo (41.15%).
Never repeat a coup with guns pointed at the people, he said, asserting that his first task was to end all the seeds of political violence after half a year of chaos under martial law.
Just three years after entering the Blue House, President Yoon Suk Yeol was ousted from power by a wave of outrage after efforts to establish martial law to extinguish anti-government protests.
The images of the army seizing central Seoul, large-scale arrests and the trial of Mr. Yoon and senior officials for "riot" have sent the whole country into a crisis of confidence.
The interim presidential Trump administration, a series of protests and a stagnant economy have plunged South Korea into an unprecedented spiral of instability since the 1980s.
As soon as the National Election Commission confirmed the victory, Mr. Lee immediately took over the power and the position of Commander-in-Chief. A simple inauguration ceremony will be held at 11:00 a.m. on June 4 (Seoul time) at the National Assembly.
The challenge awaits him at the door of the Green House: Asia's fourth largest economy is facing slowing growth, exports are threatened by protectionism - especially from the US under President Donald Trump, who has reimposed heavy tariffs on Korean cars and steel.
A report from the Center for Strategic and International Studies (CSIS) in Washington assessed: types of free time are hardly available for President Lee. A trade deal with Trump will be the first test of his leadership skills.
While the White House confirmed the election as free and fair and pledged that the US-Korea alliance would remain steady as steel, Lee Jae-myung showed a more flexible diplomatic stance.
He said he would continue the tripartite cooperation policy with the US-Japan, but emphasized the vital role of China, its largest trading partner, and avoid a tough confrontation on the Taiwan issue.
I do not pursue confrontation, I pursue the survival and development of this country, Lee said at a brief press conference.
The new president has no secret to his ambition to bring South Korea into a new growth cycle thanks to high technology and innovative investment. Financial support packages will be boosted for low-income and middle-class families - the most severely damaged forces in the recent political storm.
However, the biggest task is perhaps to heal a society deeply divided after the martial law crisis. "Damaged beliefs cannot be healed by slogans. We need time, sincerity and real action, Lee admitted.
