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. 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 (during the 20 May 2006 game involving a bench-clearing brawl) and another home run.
On July 27, 2007, he was traded to the Philadelphia Phillies for pitcherMichael Dubee. He was the first Asian-born player to join the Phillies.
On December 18, 2007, Iguchi signed a one-year deal with the San Diego Padres. He was released on September 1, 2008.
On September 5, 2008, the Phillies signed Iguchi, making it his second stint with the team. Because he was acquired after September 1, he was ineligible for the team's postseason roster, so he was not with the team when they bested the Tampa Bay Rays in the World Series, although he received a World Series ring.