In May 2006, the year he turned 18, he signed with the SK Wyverns as a third-year student at Ansan Technical High School, and in September he led Korea to the world junior baseball title and was named tournament MVP.
The breakthrough yearIn April 2007, the year he turned 19, he made his pro debut and lasted four innings, allowing three runs. On October 26, against Doosan in Game 4 of the Korean Series, he threw 7⅓ scoreless innings and became known, and in November he got the win against Chunichi at the Konami Cup.
In August 2008, he started the Beijing Olympics semifinal against Japan and held it to two runs in eight innings, and Korea won the gold medal. In November, in his second pro season, he was named regular-season MVP. In 2009, he took the loss against Japan at the World Baseball Classic, and Korea lost to Japan in the final and finished runner-up.
In 2010, he won a second wins title with 17 wins, and in October he closed out Game 4 of the Korean Series to clinch the title. In 2013, he won 10 games, the start of six straight seasons of 10 or more through 2019. In December 2014, talks with the San Diego Padres through the posting system broke down and he stayed with SK.
In 2016, he became the third lefty in KBO League history to reach 100 career wins, and in November he signed a four-year, 8.5 billion won FA contract with SK. In January 2017, he had left elbow ligament surgery and missed the season. In March 2018, he returned to the first team after 533 days, and in November he closed out Game 6 of the Korean Series.
In December 2019, he signed with the St. Louis Cardinals for two years and $8 million. In July 2020, he saved the MLB opener in his debut, and he ended the year with a 1.62 ERA. In 2021, he went 7-7 in 27 games.
In March 2022, he signed with SSG for four years and 15.1 billion won and returned to the KBO League. He went 13-3 with a 2.13 ERA as SSG won the regular season, and in November he was the last pitcher of Game 6 of the Korean Series. In 2023, he went 9-8, and in June the KBO disciplinary committee gave him 80 hours of community service and a 5 million won fine over drinking during the WBC. In 2024, he went 12-10.
In June 2025, he signed a two-year, 3.6 billion won multi-year deal with SSG, and in July he got the win in his first head-to-head start against Hyun-jin Ryu. He finished the season 10-10. In March 2026, he had left shoulder surgery, and the club expected rehab to take six months or more.
Kwang-hyun Kim (born Jul 22, 1988) made his pro debut on Apr 10, 2007, the year he turned 19, and became known on Oct 26, 2007, the year he turned 19, when he threw 7⅓ scoreless innings against Doosan in Game 4 of the Korean Series. He was named regular-season MVP in 2008, the year he turned 20, and made his MLB debut in 2020, the year he turned 32.
Ages are by calendar year (the year minus the birth year), birthdays aside.