Miyazawa began her career as a child model, seeing wide exposure as the original face of Mitsui Rehouse, and made her acting debut in the 1988 film Seven Day's War, for which she won the Japan Academy Award for Newcomer of the Year at age 16.

Her short-lived music career began with the single "Dream Rush" in 1989, and the next year she performed at the prestigious Kōhaku Uta Gassen television special.

Miyazawa quickly rose to prominence as one of the top idols of the early Heisei period, attracting controversy for her 1991 nude photography book Santa Fe, which moved 1.5 million copies.

Her personal struggles were further scrutinized, including a high-profile engagement to sumo wrestler Takanohana, a suicide attempt and battle with anorexia nervosa.

[citation needed] Tony Takitani (2004) — an adaptation of a short story by the bestselling author Haruki Murakami — received critical acclaim, with Miyazawa playing two roles alongside Issey Ogata.

[6] On February 13, 2009, Miyazawa announced to the public that she was six months pregnant and would soon marry the father of the child who is reported to be Hiroyuki Nakatsu, an ex-pro surfer from Hawaii turned entrepreneur.