The 19th South Korean presidential election was held on 9 May 2017, after the impeachment and dismissal of Park Geun-hye.[1] The election was conducted in a single round on a first-past-the-post basis.

The election was originally scheduled to be held on 20 December 2017, but was moved earlier after the decision of the Constitutional Court on 10 March 2017 to uphold the parliament’s impeachment of Park Geun-hye. In order to avoid a power vacuum, then-Prime Minister Hwang Kyo-ahn succeeded Park as the acting president. After Park was removed from the office by the Constitutional Court’s ruling, acting president Hwang indicated he would not run for a term in his own right.[2][3][4]

Source : https://en.wikipedia.org/wiki/South_Korean_presidential_election,_2017