The year he turned 24, he joined the Ulsan City Hall team and won bronze in the 75 kg class at the National Sports Festival.
In 2008, he placed second in the 80 kg class at the Mr. Korea contest. In 2010, he won the 80 kg class at Mr. University and took the Grand Prix. In 2011, he won the 80 kg class at Mr. Korea.
In 2012, he won the National Sports Festival 75 kg class and took silver at the World Bodybuilding Championships in Ecuador. In 2013, he won the National Sports Festival again and took silver in the 75 kg class at the World Championships in Morocco.
In 2014, he received the Mr. Korea Grand Prix and won the National Sports Festival 75 kg class for a third straight year. He also took silver in the 80 kg class at the IFBB Asian Bodybuilding and Fitness Championships.
In 2015, he won the National Sports Festival 75 kg class for a fourth straight year, then won gold in the 75 kg class at the World Bodybuilding Championships. In 2016, he moved up to the 80 kg class and took silver at the World Championships. In 2017, he won gold in the 80 kg class at the same event. In 2018, he introduced himself as being in his 11th year as a national team member and said he runs a private gym in Seoul. He also won the National Sports Festival light middleweight (80 kg) class that year.
The breakthrough yearThe year he turned 36, he won Classic Physique at both the pro qualifier and the pro show at the Toronto Pro Supershow in Canada, earning IFBB pro status and a Mr. Olympia qualification together. Sports Seoul wrote that it was the first Classic Physique Olympia qualification for a Korean. He tied for 16th at Mr. Olympia that September.
In 2020, he competed in the Mr. Olympia Classic Physique division again. In April 2021, he gave a lecture at Seoul Hoseo Institute of the Arts, and in October he competed in Mr. Olympia for a third straight year and tied for 16th with Yoo In-seong. In 2023, he was at the same IFBB pro show as Kim Geon-woo. When Kim Geon-woo earned pro status and an Olympia qualification together, Beyond Post wrote that Kim Seong-hwan had been the first to do so. In 2024, he was introduced as the official model of Gym80 Korea.
Kim Seong-hwan (born Oct 22, 1983) debuted in 2007, the year he turned 24, with a bronze medal at the National Sports Festival for the Ulsan City Hall team, and became known in 2019, the year he turned 36, when he won Classic Physique at the Toronto Pro Supershow in Canada and qualified for Mr. Olympia. He received the Mr. Korea Grand Prix in 2014, the year he turned 31.
Ages are by calendar year (the year minus the birth year), birthdays aside.