Moon's presidency began even before an inauguration ceremony as his election was a result of the rare by-election that sought to fill the top elected office vacated by former President Park Geun-hye.
The former conservative leader was removed on March 10 by a Constitutional Court ruling that upheld her parliamentary impeachment late last year over a series of corruption allegations that have also led to Park's arrest and indictment.
Moon's five-year term began at 8:09 am Wednesday when the National Election Commission (NEC) confirmed his victory in the election held Tuesday, the commission said. The liberal candidate from the Democratic Party secured 13,423,800 votes, or 41.08% of the total 32,807,908 votes cast, according to the NEC.
"President Moon Jae-in began his official term as the 19th president as he exercised his legal authority as the commander in chief at 8:09 am on May 10," the presidential office said in a press release.
He was scheduled to meet with the leaders of all five parliamentary parties, starting with Rep. Chung Woo-taik, floor leader and interim chief of the conservative Liberty Korea Party, which has now become the main opposition party as the result of the election.
Following his meetings, Moon was set to attend a scaled-down inauguration ceremony at the National Assembly.
Then after that, he is scheduled to hold his first press conference as president at the presidential office of Cheong Wa Dae to announce his nominees for four key government and Cheong Wa Dae posts, including prime minister and chief of staff.
