Yamaguchi was born inSakawa, Kochi on April 17, 1978. He joinedJEF United Ichihara (laterJEF United Chiba) from youth team in 1996. He debuted on March 20, when he was 17 year and 354 days old. It was the youngest player to play forJ1 League untilYuki Abe made new record in 1998. He became a regular player as center back from 1997. He moved toGamba Osaka in 2001. The club won the champions2005 J1 League,2007 J.League Cup,2008 and2009 Emperor's Cup. He was also elected Best XI for 3 years in a row (2006-2008). In Asia, in 2008, the club won the championsAFC Champions League and the 3rd placeClub World Cup. He returned JEF United Chiba in 2012 and played in 3 seasons. He moved toKyoto Sanga FC in 2015 and retired end of 2015 season.
On May 27, 2009, Yamaguchi debuted forJapan national team againstChile. On May 31, he also played againstBelgium. He played 2 games for Japan in 2009.[2]
From 2021 season, he will be the assistant coach ofShonan Bellmare on 14 May 2021.[3] On 1 September 2021, Yamaguchi was appointed as manager of J1 club,Shonan Bellmare following the retirement ofBin Ukishima for during 2021 season. After winning his first victory as a manager in the 33rd round againstYokohama FC. On October 23 at same year, he led the team to remain in the final round of the 38th round againstGamba Osaka on December 4 at same year. It was decided that he would continue to serve as manager in the 2022 season and in June he was awarded the monthly best manager award.
