Born and raised in Edogawa, Tokyo, he joined the Japanese talent agency, Johnny & Associates, at the age of 12.

[2] An avid baseball fan and player like the character he was named after, Kamenashi once represented his country in the junior world league as shortstop though he had to give up the sport professionally due to lack of spare time after he was accepted into Johnny's Entertainment despite having the support of Johnny Kitagawa, the agency's president, to pursue both careers.

[7] Kamenashi also made his film debut on July 11, 2009, reprising his role of Ryū Odagiri, now a trainee teacher in Gokusen The Movie.

[10] In 2010, he was cast in the leading role of Kyohei Takano for a live-action adaptation of popular manga, Yamato Nadeshiko Shichi Henge, which aired on NTV.

In 2017, he appeared in the drama Boku unmei no hito desu alongside his former co-star from Nobuta wo produce, Tomohisa Yamashita.

[17] In 2010, Kamenashi won the annual Best Jeanist award with more than 29,000 votes in the men's category, almost triple that of the second runner-up, Masaki Aiba.

This is his fifth consecutive win and is thus promoted into the hall of fame, making him Eternal Best Jeanist and ineligible for future runs.

[19][20] Kamenashi participated in the Central League's Yomiuri Giants 23rd FanFiesta 2009 on November 23, 2009, and led his team to victory.

[21] In 2012, he was given the opportunity to do live coverage of Major League Baseball between Oakland Athletics and Yomiuri Giants.

In the post, a stuffed turtle, a classic image linked to him because of the kanji in his last name, invites fans to follow him.