President Lee Jae-myung formally began his five-year term Wednesday after the National Election Commission confirmed his election victory.
Lee assumed the presidency at 6:21 a.m., following the NEC's approval of his win during a plenary session.
He takes office immediately without a transition period, as the snap election was held Tuesday to replace former President Yoon Suk Yeol, who was ousted over a failed bid to impose martial law.
He assumed presidential duties, including the role of commander-in-chief, from acting President Lee Ju-ho.
Lee, the liberal Democratic Party candidate, won the election with 49.42 percent of the vote, defeating his conservative People Power Party rival Kim Moon-soo, who received 41.15 percent.
DP floor leader Park Chan-dae is set to collect the official certificate of election from the NEC office in Gwacheon, just south of Seoul.
On the first day, Lee will be sworn in during a scaled-down inauguration ceremony at the National Assembly at 11 a.m.
Prior to the ceremony, he plans to pay tribute at Seoul National Cemetery. (Yonhap)
