Junko Mihara was born on September 13, 1964 in Itabashi ward Tokyo Japan, as a second child of Kayoko and Nobuo Mihara who owned a metal plating business. Junko was a quiet girl, and to encourage her to be more self expressive, when she was seven, her mother entered her into a stage production company called Gekidan Fuji. Although she starred in many stage productions, her introverted nature continued. She used to stay home and listen to songs sung by Momoe Yamaguchi who she idolized. She didn't have many friends but she was viewed as a leader in her class and many girls came to her when they got bullied by boys. When she was 14, she made a debut in TV drama "Moero Attack" which was about high school volley ball team. While most other actors were in their twenties acting as high school girls, Junko was actually attending middle school but looked just as mature as the other actors. The same year she was chosen to play what was to become her defining role in the TV series "Sannen B gumi Kinpachi Sensei". Junko played the role of a delinquent school girl Reiko Yamada in this series which won her many accolades for her acting. Junko took the role because the part of acting a delinquent school girl reminded her of her idol Momoe Yamaguchi (not that Yamaguchi was a delinquent, but Yamaguchi's strength of character was what she wanted to emulate). During this time she was busy with both school and work, and she proclaims that she only went home to take a bath and had no time to even sleep. She says "Kinpachi Sensei" was more like her real school than the actual school she was attending. When she was 15 she also made her debut as a singer with the song "Sexy Night". At the age of 16, Junko bought a house for her parents with the proceeds she's made from her acting and singing career. In 1972, she was cast in a starring role in "Aa, Nomugi Tohge Shinryoku Hen". She was elated to be chosen for this lead role because in acting her idol was Shinobu Otake who starred in the original "Aa, Nomugi Tohge". Even now she claims that this is her defining movie.
Junko started to enter car racing when she was 22 as a hobby. She experienced few accidents which she claims she has broken bones in seven different locations. She married a race car driver who was her instructor, but divorced him nine years later. She continues to star in many TV, and stage dramas and has hope to lead a company of stage actors one day.