The 21-year-old, who has made 13 appearances for the national team, is regarded as one of the brightest stars in the K-League. Gyeongnam are believed to have received a fee in the region of £1.28 million for his services.
"We have signed Yoon Bitgaram to be part of our challenge to win the K-League and the 2012 AFC Champions League," Seongnam said in a statement. "Naturally, he will strengthen the team and help us increase our fan base."
Yoon, who captained South Korea's team at the 2007 Under-17 World Cup and subsequently spent time training with Blackburn Rovers, played 61 games for Gyeongnam.
In two seasons at the club, he scored 17 goals and recorded 14 assists. Such form led him to be named as the K-League's Rookie of the Year in 2010 and he made the league's best XI in 2011.
Seongnam have been drawn in Group G of the 2012 AFC Champions League and will face China's Tianjin Teda, Central Coast Mariners of Australia and Japan's Nagoya Grampus.