A pianist by training, Karen Tanaka began studying composition at the age of ten. In 1982 she entered the musical school Toho Gakuen, trained with Akira Miyoshi and notably won the Japan Symphony Foundation Award. She completed her training formation in Paris, France, with Tristan Murail (1986), then in Florence, Italy, with Luciano Berio (1990–1991). She subsequently took part in the composition and computer music course at Ircam (1991–1992).

Karen Tanaka composes mainly for instrumental formations, from soloist to the orchestra, and also employs electro-acoustic techniques. She has taught in the United States (Universities of California, Santa Barbara and Michigan) and has co-directed the Yatsugatake Kogen Music Festival. Her works include Anamorphose (Prix Gaudeamus 1987), Initum for orchestra and electronic instruments (1993), Invisible Curve (1996), Water and Stone (1999, first performed at Radio France) and Urban Prayer for cello and orchestra (2004, premiered at the University of Berkeley).