Lee won one distances and became second overall at the 2008 World Junior Championships in Bolzano. He won 2009-2010 Overall World Cup. At the 2010 Olympic Winter Games in Vancouver, Lee won two gold medal in the 1000m and 1500m events.
On the other hand, Lee's parents had a financial difficulty in supporting their children's dream. They had to spend over 2,000,000 won (approximately 1,736 dollars) per month for the fees of skating lessons, purchasing skating tools and renting exercising locations. Although Lee's parents worked together, spent all savings and even sold paddy fields in a countryside to support their children, that was not enough to cover all. They finally had to loan mortgages on their house where the family was living. However, Lee's sister eventually gave up due to the financial situation and tried to seek her future in other sport genres that cost less money for training such as inline skating and wakeboarding. The fact that his sister had to drop her dream has stimulated Lee Jung-Su to focus on the skating training.
Lee has been handed a 3-year ban along with his team mate Kwak Yoon-Gy for controversial foulplay. Lee had written a note stating that he was not fit to compete in the World Championships 2010 Sofia, because of an injury. This turned out to be not true, and Lee admitted that his coach forced him to pull out so that he could give team mate Kwak Yoon-Gy a chance to win a medal. Kwak Yoon-Gy went on to win Gold in the 1500m.