Originally a bantamweight (under 63 kg), Lee temporarily went down in weight to flyweight (under 58 kg) after the 2011 World Championships in order to compete in the 2012 Olympics, where there were only four weight classes. Lee made his international flyweight debut at the 2011 World Taekwondo Olympic Qualification Tournament in Baku, Azerbaijan where he had his first international loss to 2008 Olympic silver medalist Gabriel Mercedes 14–12 in the semifinals. In May 2012, however, he captured his first flyweight gold medal at the 2012 Asian Taekwondo Championships, beating reigning Asian flyweight champion Pen-Ek Karaket 8–4 in the final bout. At the 2016 Summer Olympics Lee won a bronze medal, beating Jaouad Achab from Belgium 11–7. In 2016 WTF World Taekwondo Grand-Prix, Lee won gold against Konstantin Minin.