After graduating from Doshisha Girls' School (Ordinary Department) in 1926, she traveled alone to the United States at the age of 17, where she pursued her studies at the University of Washington and the Eastman School of Music Graduate Department. From 1932 to 1933, she studied composition under Paul Hindemith at the Berlin State Academy of Music. In 1942, she won 3rd prize in the composition division of the 11th NHK-Mainichi Shimbun Music Competition. In 1949, she became a professor at Doshisha Women's College of Liberal Arts after serving as a lecturer at Doshisha Women's Vocational School. In 1950, "A Musician's Aesthetic Confession" (Taika Shobo), a book authored by Leonid Kreutzer and translated by NAKASEKO Kazu, was published. In 1951, she received the Mainichi Music Special Award.

While known for introducing contemporary music to Japan and for her achievements as an educator, she also composed piano pieces, vocal works, choral works, chamber music, orchestral works, and sacred music. Approximately 50 autograph scores were discovered and organized by the Doshisha Women's College of Liberal Arts Archives Center more than forty years after her death, and are now preserved in the Doshisha Women's College of Liberal Arts Library. Furthermore, NAKASEKO Kazu herself was a devout Christian who felt a sense of incongruity with hymns sung in Protestant churches, which often involved setting Japanese lyrics to Western melodies. She therefore worked to create beloved hymns that incorporated the intonation of the Japanese language.