Joruta Kosugi was born on December 19, 1957, in Kanagawa. Kosugi came from a family of physicians but he become more interested in medias. Thus, he majored in the Department of Broadcasting at the Japanese College of Arts. However, he failed the examination to become a radio announcer and worked for 4 years as a salaryman.
By chance, Kosugi was hired to narrated an advert for Takara's "New Game of Life". Through his connection with the director of the advert, Kosugi began to work as a voice actor mainly doing narration work. However, he eventually obtained a role as Captain Henken in the TV anime Mobile Suit Zeta Gundam. Kosugi juggled between his two activites for a while before being told to focus on one career and thus he committed himself to become a voice actor.