Domoto Koichi joined Johnny's Entertainment at the age of 12. His sister sent in his application for him. He is a member of the duo KinKi Kids with fellow Johnny's member Domoto Tsuyoshi and has a solo career since 2006. He has been in the musical Endless SHOCK for the last seven years and has also been in many doramas.
Born in Ashiya, Hyōgo, Japan, Domoto joined the Japanese talent agency Johnny & Associates at the age of 12 after his sister sent in his application without his knowledge. Domoto and his bandmate Tsuyoshi Domoto first worked together as backdancers for Hikaru Genji, who were holding a concert at Yokohama Arena, and has since then been partnered up for magazine photoshoots, music acts and drama projects. The duo eventually made their debut in 1997 with a double release of a single "Garasu no Shōnen" and an album A Album, both of which went on to sell over a million copies.
In July 2007, after five years, Domoto starred as the lead in a drama entitled Sushi Ōji!. With kōhai Yuichi Nakamaru of KAT-TUN playing the role of his partner, he played the role of a martial artist training in the art of sushi. In addition, about a month before the release of the drama, it was announced that Domoto would star in the movie sequel to Sushi Ōji. It was Domoto's first time starring alone in a movie, and his first movie appearance since the 1994 movie Ienaki Ko. In 2008, it was announced that Domoto would not only reprise his role for the sequel to Sushi Ōji!, Ginmaku Ban Sushi Ōji!: New York e Iku, but he would also provide the theme song, marking his first time as a solo artist to sing a theme song for a movie. In April 2008, Domoto's long-running musical Endless Shock was awarded the Grand Prize of the 33rd Kazuo Kikuta Drama Awards for theater. Later that month, Domoto traveled to New York to attend the American premiere of his Sushi Ōji! movie, which was screened at the Walter Reade Theatre.
2009 saw Domoto's first solo single release in nearly three years. Titled "Ayakashi", it topped the Oricon charts by selling 151,000 copies in the first week of its release.
On September 1, 2010, Domoto released BPM, his first solo album in four years. He will also begin his solo tour on September 11, 2010.