Born in Nara, Domoto joined Johnny's Entertainment on May 5, 1991, which also the first time he met his future bandmate Koichi Domoto. The opportunity came while without his knowing, his mother and his 6-years-older sister sent his resume to the office. Domoto and his bandmate Koichi 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 starred in their first drama together called Ningen Shikkaku in 1994, in which Domoto was awarded Best Newcomer in the Television Drama Academy Awards.
With Koichi Domoto, he eventually made his debut in 1997 as KinKi Kids with a double release of a single "Garasu no Shōnen" and an album A Album, both of which went on to sell more than a million copies.
On May 29, 2002, Domoto released his first solo single, "Machi/Dekiai Logic", in which he penned and composed all the tracks. The single was used as the theme song for Domoto's lead-role drama Yume no California and it reached number 1 in the weekly chart. In the following month, Domoto started his career as an illustrator by publishing a book in collaboration with writer Shizuka Iziyuuin. They collaborated again for another book in 2003.
Domoto appeared in the 2003 drama Moto Kare, in which he co-starred for the second time with Ryoko Hirosue after their hit drama Summer Snow in 2000. In April 2004, Domoto once again provided the theme song for his lead-role drama Home Drama. This year, he won the 'Best Jeanist' award. The following year, Domoto acted in a movie, Fantastipo, with fellow Johnny's personality Taichi Kokubun. He paired with Toraji Haiji to release the theme song for the movie. The same year, Domoto starred in Hoshi ni Negai o (a.k.a. Wish Upon A Star), a TV drama produced by Disney and Fuji TV based on the true story of planetarium engineer Takayuki Ohira who designed Megastar II — the world's most advanced planetarium projector.
In 2006, Domoto put his acting career on hold and focused more on his music career. He began to release his solo work under the project name ENDLICHERI☆ENDLICHERI. During his ENDLICHERI☆ENDLICHERI era, Domoto released three singles which all topped the weekly charts and made him the second male soloist after Masahiko Kondo to have achieved five consecutive number one singles. He then renamed his solo project 244 Endli-x (pronounced "Tsuyoshi Endorikkusu") in 2008. He announced that he would go on his first concert tour as 244 Endli-x soon after, which began on March 29, 2008 at the Yokohama Arena and ended in Sendai on May 8, 2008. At the end of April, Domoto was appointed to be the first special ambassador for Nara tourism.
Domoto once again changed his solo project name in 2009 to Tsuyoshi (剛紫?) and simultaneously released a single and an album on his birthday, April 10. In the same year, he released another single, "Rain", on September 9, which topped the Oricon Single Weekly Charts. Domoto also announced his collaboration with the hat brand CA4LA. Known as the fashion leader with unique style, Domoto was chosen by famous sports brand Adidas Originals to be the image character for its new campaign BE Originals which start on February 12, 2010.
On April 6, 2011, Domoto released his ninth single, "Eni o Yuite", which was recorded at shrines believed to have connections to Nara's entertainment and music industries. Another single, "Niji no Uta", was released in September 2011.