Due to her father's work, Kajiura lived in West Germany since 1972 and until her middle school years. Her first music piece, which she had written at the age of 7, was a farewell song for her grandmother. After graduating from college (back in Tokyo), she began working as a systems engineering programmer, but in 1992, she turned her career around to focus on her activities on music. She admits that it was her father who greatly influenced this decision, for he was a great opera and classical music admirer.
In July 1992, she made her debut in an all-female trio See-Saw, then consisting of Chiaki Ishikawa (lead vocals), herself (back-up vocals, keyboards), and Yukiko Nishioka. In the following two years, the group released six singles and two albums but in 1995 they temporarily broke up. Nishioka decided to become a writer while Kajiura carried on with her solo musician career, composing music for other artists as well as sound producing for TV, commercials, films, animation and games.
In 2001, she and Chiaki Ishikawa reunited as See-Saw. Around the same time she became involved with Koichi Mashimo's animation studio Bee Train and their first widely popular project, Noir. Despite the series' controversial status among the reviewers, all critics generally praised its OST as a breakthrough in the animation music scene for its risky but highly successful mix of synth, opera, and French-flaired sound.
In 2009, Fiction Junction returned to perform the opening themesong to Pandora Hearts, Parallel Hearts, with The majority of the show's music composed by Yuki Kajiura.