In 2004, he led his team to the first national championship ever, pitching four-consecutive complete game victories in the tournament with a 0.96 ERA, and was named MVP.

Although his performance was inconsistent, he showed signs of promise as a rookie, including pitching a one-hit victory in 71⁄3 innings over the Doosan Bears, facing MVP Daniel Rios in the 2007 Korean Series.

[6] When the start of the 2020 Major League Baseball season was delayed by the COVID-19 pandemic, Kim considered returning to Korea to be with his family.

[7] On July 24, 2020, Kim made his MLB debut against the Pittsburgh Pirates, allowing 1 earned run over 1 inning of work.

In 2021, Kim appeared in 27 games (21 starts) and posted a 7–7 record with a 3.46 ERA, 80 strikeouts and 39 walks in 106+2⁄3 innings.

[11] On June 1, 2023, South Korea baseball began an investigation of Kim and two other WBC pitchers (Lee Yong-chan and Jeong Cheol-won) for violating behavioral codes.

Kim tossed a five-hit complete game shutout to lead South Korea to a 1–0 victory over Chinese Taipei in the quarterfinals, and pitched two wins over Canada in the semifinals and USA in the final.

There he helped his team win a spot in the Beijing Summer Olympics by starting two times and going 2–0 with a 1.64 ERA.

In the semifinal game against Japan, he gave up one earned run and six hits in eight innings for Korea to get the victory.

Kim did not allow a runner past first base after the 3rd inning, when Japan scored on a walk, a sacrifice and a single by Norichika Aoki.