Olympic record holder in men's 200-meter breaststroke
Time / 2:07'22
Personal record in men's 200-meter breaststroke
Time / 2:06'67 (World's fourth-fastest time)

He was born in Oita in 1997.
He started to learn swimming from the second grade of elementary school. When he was a third-grade junior high school student, he entered the 51st National Junior High School Swimming Championship and the 66th National Athletic Meet.
In 2012, he entered Oita Prefectural Saiki Kakujo High School and cut a figure in swimming.
He represented Japan at Nanjing 2014 Youth Olympic Games and won a gold medal in men's 200-meter breaststroke.
In 2015, he was admitted to Faculty of Sport Sciences of Waseda University.
In 2016, he won the second place at the 92nd Japan National Championships by defeating Olympic medalists Kosuke Kitajima, Ryo Tateishi, which granted him the chance to become one of the Japanese representatives at the Rio 2016 Olympic Games. He set a new Olympic record of 2:07'22 in the men's 200-meter breaststroke semi-final at the Rio 2016 Olympic Games.
In January 2017 at the 10th Kosuke Kitajima Cup in Tokyo, he became the new record holder in men's 200-meter breaststroke with a time of 2:06'67.
In July 2017 at the 17th FINA World Aquatics Championships, he represented Japan and won a bronze medal in men's 200-meter breaststroke.
In 2018, he won a gold medal in men's 200-meter breaststroke at the 13th Pan Pacific Swimming Championships which was his first gold medal at major championship. In the same year, he became one of the Japanese representatives in swimming at the 18th Asian Games and won a silver medal in men's 200-meter breaststroke.
Ippei Watanabe graduated from School of Sport Sciences, Waseda University in March 2019 and signed to Toyota Motor Corporation. He participated in The 95th All Japan Swimming Championship held in April 2019 and claimed his first victory in this championship. He will be one of the Japanese representatives to compete at The 18th FINA World Aquatics Championships which will be held in July 2019.
He participated in The 18th FINA World Championships in July of the same year winning bronze medals of The FINA World Championships twice in a row. 【On this championship, Anton Chupkov (Russia) set a new world record of 2:06'12 breaking Ippei Watanabe's record (2:06'67).】
In December 2020, he ranked first in men's 200m breaststroke event of JAPAN SWIM 2020, scoring two consecutive wins in this contest.