Upon graduation from high school in 1999, he chose to play college baseball at Korea University instead of turning pro directly. Lee was soon regarded as one of the best offensive amateur catchers in the nation, becoming a fixture in the starting nine in his first collegiate season. In his freshman year at Korea University, he was called up to the South Korea national baseball team, and participated in the 1999 Intercontinental Cup. In Korea's first game of the round-robin tournament against Cuba, he led his team to a memorable 4-3 victory, which was South Korea's first victory over Cuba at international baseball competitions organized by the IBAF.
Signed by the Hyundai Unicorns in 2003, Lee started his pro career as a catcher. Although Lee immediately became one of the most reliable and consistent hitters in the team, he failed to make an impact with the Unicorns as a catcher due to his defensive deficiencies. So, the team convinced Lee to convert to the outfield in spring training 2006. As the 2006 season started, the team finally moved Lee to the outfield permernantly.
In the 2006 season, he finished second in batting average (.322), tenth in RBI (66) and sixth in hits (135), and was selected to the All-Star team and won his first KBO League Golden Glove Award. After the season, he was selected for the South Korea national team and competed in the 2006 Asian Games held in Doha, Qatar.
In the 2007 season, he finished ninth in batting average (.313) and sixth in hits (137).
In March 2009, Lee was called up to the South Korea national baseball team for the 2009 World Baseball Classic. He appeared in 7 games, but mostly served as a pinch runner and backup center fielder. In the 2009 KBO season, Lee had another impressive performance. He batted .311 (eighth in the league) and posted career-highs in hits (142), home runs (15), doubles (26), RBI (66), runs (84) and stolen bases (43). Lee finished third in stolen bases (43 in 51 attempts) and his stolen base percentage (.843) was higher than title-winner Lee Dae-Hyung and runner-up Jeong Keun-Woo.
On December 11, 2009, he won his second Golden Glove Award as an outfielder.[1]
On May 18, 2017, he won the game against Hanwha by hitting the first pinch-hitter-ending grand slam in the KBO league against Jung Woo-ram.[2]
In 2018 Lee was suspended 36 games for the 2019 season by the league because of an earlier (May 2015) incident in which he struck a younger teammate, Moon Woo-ram, in the face with a bat multiple times, leaving him with a concussion and serious swelling in the face. Lee said that he had hit Moon because he didn't follow his order of getting a haircut.[3]
^Kang Ae-ran (April 21, 2022). "이승엽·박용택 등 레전드 총출동…예능 '최강야구' 상반기 방송" [Lee Seung-yeop, Park Yong-taek, etc. Legends all dispatched… 'Strongest Baseball' broadcast in the first half of the entertainment show] (in Korean). Yonhap News Agency. Retrieved April 21, 2022 – via Naver.
