Lee started playing football at Komine FC and later moved to Yokogawa Electric. In 2001, he joined FC Tokyo youth team and took second places at All Japan Club Youth Soccer tournament, Prince Takamado Cup and J.League Youth tournament. He briefly joined training squads for the SouthKorea U-19 and U-20 teams but not played at official games. He experienced severe discrimination from Korean teammates referring to him as a ban-jjokbari with strong racial undertones. He was promoted to FC Tokyo in 2004 and moved to Kashiwa Reysol in 2005 and later joined Sanfrecce Hiroshima in 2009.
On 11 January 2012, Lee secured a work permit to allow him to play for Southampton, who confirmed the free transfer on 25 January 2012. He made his debut for Southampton on 28 January 2012, as a substitute in a fourth round FA Cup match against Millwall. Lee started and played the duration of the replay, failing to score as Milwall won 3–2 after a 92nd-minute winner from Liam Feeney. He scored his first goal for Southampton in a 4–0 victory over Derby County on 18 February, with a "venomous strike into the far corner" of the goal. He made his first league start one week later, a 3–0 victory away at Watford, with Lee winning a penalty for the third goal from Rickie Lambert. He has not played since 10 March 2012, after damaging ligaments and missing the rest of the season. His goal won the Southampton's Goal of the Season Award. After 5 months out injured, he made his return to action with a goal in a 4–1 victory at Stevenage in the League Cup. He was handed the number 19 shirt for the 2013–14 season after Southampton invited him back to the First Team. He made his first return to the Southampton team after year when starting in the League Cup against Bristol City. On 14 January 2014 he was released from his contract at Southampton after a two-year spell.
Return to Japan
On 14 February 2013, Lee returned to his former club, FC Tokyo on loan until the end of June. He made his debut on 2 March 2013, coming on as a 72nd-minute substitutee. He scored his first goal for the club on 23 March 2013 in the 77th minute against two-time defending champion Kashima Antlers.
In August 2008, Lee was selected Japan U-23 national team for 2008 Summer Olympics. At this tournament, he played all 3 matches. After becoming a regular starter for Sanfrecce and finishing the 2010 season strongly, Lee was rewarded with a call-up to Japan's 2011 Asian Cup squad and made his full international debut on 9 January2011 against Jordan. His first international goal was dramatic, coming as it did in the 109th minute of the final to secure a 1–0 win over Australia and Japan's fourth Asian Cup success.
