Iguchi began playing in high school and after graduating in 1993, went to Aoyama Gakuin University where he distinguished himself by hitting the Tohto University Baseball League record of eight home runs in a season and winning the triple crown. He was a member of Japanese National Team in 1996 Summer Olympics that won the silver medal. He was the first pick in the 1996 draft by Fukuoka Daiei Hawks.
In his debut year of 1997, he hit a grand slam in the first game of his professional career. He suffered a shoulder injury in the 2000 season and had a surgery which ended his season. He recovered fully in 2001 hitting 30 home runs and leading the league with a personal best 44 stolen bases. In 2003, he hit over .300, had over 100 RBI and led the league in steals. He left Fukuoka Daiei after the 2004 season to play for the Chicago White Sox. He maintains a friendship with his former teammates Kenji Johjima and Koji Akiyama.
During the 2005 MLB season, he had a .278 batting average with 15 home runs and 15 stolen bases. In the 2005 Divisional Series, he hit a go-ahead 3-run home run in Game 2 against the Boston Red Sox.
In 2006, Iguchi had two multi-homer games, both times hitting a grand slam and another home run.
He is the first everyday Japanese player to play on a World Series-winning team. (Hideki Irabu was on the New York Yankees 1998 World Series roster and got a ring, but did not appear in a World Series game.)