At the age of 12, she traveled to London to study dance at the Royal Ballet Academy.

In 1971, Momoi debuted in director Kon Ichikawa's Ai Futatabi (To Love Again).

As an actress, she has worked with directors including Akira Kurosawa (Kagemusha, 1980), Tatsumi Kumashiro (Seishun no Satetsu, 1974), Yoji Yamada (The Yellow Handkerchief, 1977 and Otoko wa Tsuraiyo, 1979), Shohei Imamura (Why Not?, 1981), Shunji Iwai (Swallowtail Butterfly, 1996), Jun Ichikawa (Tokyo Yakyoku, 1997), Mitani Koki (Welcome Back, Mr. McDonald, 1997), Yoshimitsu Morita (Like Asura, 2003) and Takashi Miike (Izo, Sukiyaki Western Django).

She performed in The Sun (2005) directed by Alexander Sokurov and appeared in director Rob Marshall's film Memoirs of a Geisha.

Momoi has pursued various projects in producing, directing, screenwriting, and design in addition to her acting.