Gackt was born Gakuto Oshiro in Okinawa, Japan. His father was a music teacher, and his mother also a teacher. He is the second of three children, with an older sister and younger brother.
His musical education began early, and he started learning classical music theory and piano from the age of three. After exposure to rock music during his teenage years, he practiced electric guitar and drums intensely. In the early 1990s he was working as a sound technician and studio drummer, but by the mid-'90s he had begun his career as a singer. He spent a short time in the independent band Cains:Feel before moving on to the visual kei rock band Malice Mizer. With Gackt as vocalist, lyricist, and composer, they rose to fame within the visual kei genre. In 1999 he parted ways with the band and launched his solo career, debuting with the EP Mizérable. He has since released nine studio albums, eight compilation albums, and forty-four singles. He has toured extensively within Japan and also throughout Asia and Europe.
With an illustrious career spanning over 15 years, and forty-three consecutive singles ranked in the top ten of the Oricon music charts, he holds the title of the most successful male soloist in Japanese music history. A hallmark of his productions has been the use of all-encompassing, conceptual, and sometimes abstract themes, "Moon" and "Requiem et Reminiscence", to develop a series of related songs, concerts, movies, books or theatre play. To describe this idea he combined the words visual, live (concert), and alive to form the term "Visualive". It references the evocative and immersive experience he strives to create for his audiences.
In addition to his music career, Gackt has undertaken various film and television acting roles. He wrote and starred in his first cinematic production Moon Child (2003), which screened at the Cannes Film Festival in 2003, and the Philadelphia Film Festival in 2004. In 2007 he received a TV Navi award for best supporting actor in a drama, for his portrayal of the powerful feudal leader Kenshin Uesugi in NHK's The Trusted Confidant (2007).
One of Gackt's most notable performances was as the samurai protagonist Yoshi in the Guy Moshe film Bunraku (2010), where he costarred alongside Josh Hartnett, Woody Harrelson, Ron Perlman and Demi Moore. His depiction of the unnerving eunuch Jo Teigai in NHK's TV drama Tempest (2011) was brought to movie screens the following year in Gekijouban Tenpesuto 3D (2012). Recently he reprised his role as both Takashi Shiki and Yumeoji (dream prince) from the television drama Akumu chan (2012) in the cinematic release, Akumu Chan the Movie (2014).
Gackt's numerous voice acting credits include animated films, such as Dragon Age: Dawn of the Seeker (2012), and video games, with two from the popular Final Fantasy VII series; Dirge of Cerberus: Final Fantasy VII (2006)and Crisis Core: Final Fantasy VII (2007) among others.
In his stage play debut Nemuri Kyoshiro Burahikae (2010), Gackt was cast as the leading character. He later expanded his theater credentials by resuming his "Moon" concept and writing, producing, composing and starring in Moon Saga - Yoshitsune Hiden (2012). He has since announced a sequel scheduled to begin in August 2014 entitled Moon Saga - Yoshitsune Hiden - Chapter 2 (2014).