As a teenager she made her feature film debut in the 1995 Shunji Iwai film Love Letter playing the role of Itsuki Fujii as a young girl. The film was a huge box-office success and Miki picked up a number of awards for her role including a Japanese Academy Award for 'Newcomer of the Year'.

She also starred in Hagusen nagashi (1996) on TV as well as in numerous other television series and movies. Miki's portrayal of the character Tomie in the 2001 horror movie Tomie: Re-birth was one of the more popular interpretations of the role.

In January 2008 Miki Sakai appeared in the 10-hour long TV historical drama Tokugawa Fūunroku Hachidai Shōgun Yoshimune.