Cho Kuk, leader of the minor progressive Rebuilding Korea Party, speaks to reporters at his campaign office in Pyeongtaek, Gyeonggi Province, early Thursday after conceding defeat in the parliamentary by-election for the Pyeongtaek-B constituency. Yonhap

Cho Kuk, leader of the Rebuilding Korea Party (RKP), failed in his bid to return to parliament in the by-election held alongside Wednesday's local elections, dealing a heavy blow to his political career.

According to the National Election Commission, main opposition People Power Party (PPP) candidate Yoo Ui-dong won the by-election for the Pyeongtaek-B constituency in Gyeonggi Province with 34.83 percent of the vote, based on vote-counting results as of 8:30 a.m. Thursday.

Ruling Democratic Party of Korea (DPK) candidate Kim Yong-nam came in second with 28.77 percent, while Cho came third with 27.24 percent.

Cho conceded defeat at his campaign office around 3 a.m. after Yoo's victory became certain.