Yamaguchi has competed at the
World Men's Curling Championships six times in his career. At the
2009 Worlds in
Moncton,
New Brunswick, Canada, he played third for the Japanese team, which placed tenth in the tournament; At the
2013 Worlds in
Victoria, British Columbia, Canada, he played third for the Japanese team, which placed 11th in the tournament; At the
2014 Worlds in
Beijing, China, he played third for the Japanese team, which placed fifth in the tournament; At the
2015 Worlds in
Halifax,
Nova Scotia, Canada, he played as third for the Japanese team, which placed sixth in the tournament; At the
2016 Worlds in
Basel, Switzerland, he played second for the Japanese team, which placed fourth in the tournament; and at the
2017 Worlds in
Edmonton,
Alberta, Canada, he played second for the Japanese team, which placed seventh in the tournament. He played second for
Yusuke Morozumi rink and represented Japan at the
2018 Winter Olympics, finishing in 8th place.
Mixed doubles Yamaguchi represented Japan with
Satsuki Fujisawa at the
2018 World Mixed Doubles Curling Championship, finishing in 5th place. The pair again represented Japan at the
2019 World Mixed Doubles Curling Championship, finishing in 5th once again. In 2024, Yamaguchi partnered with
Miyu Ueno, and in their first year together, won the
Japan Mixed Doubles Curling Championship. The pair represented Japan at the
2024 World Mixed Doubles Curling Championship, finishing the round robin at 6–3 and in 9th place. Due to their win at the 2024 national championships, the pair also qualified for the
2025 Japanese Olympic mixed doubles curling trials. At the national Olympic trials, the team finished a disappointing 0–4. ==Personal life==