Lee Jang-Soo was one of the first players to play professional football in South Korea when he started his professional football career at Yukong Elephants in 1983 with the formation of the K-League. Despite already being in his late twenties he would eventually play in 53 league games in his professional career which ended in 1986.
After his football career he became a coach at Honam University before being offered the chance to become a trainer with the newly formed Ilhwa Chunma team in the K-League. He was offered a promotion as a coaching in 1992 where he was part of the team that took them second in the league. The next few seasons saw him as part of the coaching team that would establish Ilhwa Chunma as a successful team within the K-League by winning the league for three consecutive seasons. In the 1996 league season when Ilhwa Chunma decided to rename themselves as Cheonan Ilhwa Chunma, Lee Jang-Soo was again promoted to the Head coach position after the previous manager Park Jong-Hwan left, however after a disappointing season where they were never in the title challenge Lee Jang-Soo left.
Throughout 1997 Lee Jang-Soo went to Brazil to study coaching abroad until 1998 when Lee Jang-Soo would move to China and manage Chongqing Lifan for four seasons. While he was there he managed to twice take Chongqing Lifan to fourth in the league in the 1999 and 2000 league season. However it wasn't until 2002 when Lee Jang-Soo had moved to Qingdao Beilaite that he rose to prominace within China and won the Chinese FA Cup with them. The following season though Qingdao Beilaite were to have a disappointing season when they finished the league in eleventh and Lee Jang-Soo would return to Korea. Back in South Korea Lee Jang-Soo would quickly find a team to coach with Chunnam Dragons and subsequently FC Seoul where he led them both to a Championship playoffs spot.
At the beginning of the 2006 league season Lee Jang-Soo returned to China with Beijing Guoan who required a manager after Shen Xiangfu left after a disappointing season. Under Lee Jang-Soo, Beijing Guoan immediately improved by coming third in the league. Despite the team's continued improvement within the league and a successful start in the 2009 Chinese Super League season where the club were currently leading the table on September 16, 2009, Lee was fired by Beijing Guoan for not using particular players that were favored by the club directors.
On 25 March 2010, Lee was hired by Guangzhou Evergrande, who was newly relegated to China League One for match-fixing scandal, as the team's new manager. He led Guangzhou to finish first place in the 2010 League One season and won promotion back to the top flight at the first attempt. In his second season, Guangzhou Evergrande won the Super League title for the first time in the club's history. He also set the club's record for longest unbeaten streak in the league with 32 wins and 12 draws, which was ended on 18 September after losing to Changchun Yatai 2–1.