Juno was born in England into a showbiz family. Her mother is a producer, Amanda Temple, and her father is the film director, Julien Temple. She was named 'Juno' after her parents took a visit to the Grand Canyon, during pregnancy, and found they were standing on a butte of Cape Final known as Juno Temple.
Her family moved to America, where she spent the first 4 years of her life. The family then moved back to England and settled in Somerset.
At age 4, she decided she wanted to be an actor after her father showed her Belle et la Bête by Jean Cocteau.
She attended Enmore Primary School in Somerset. It was during this time that her father cast her in his film Vigo: A Passion for Life (1998). However, her father ended up cutting her out of the film. Two years later, age 11, her father cast her in another of his films, Pandaemonium (2000).
She became a weekly boarder at King's College boarding school in Taunton. She then moved on to Bedales boarding school in Hampshire to take her A-Levels, one of which was Drama. She left with a B and two C's.
At age 15, she told her parents that she was serious about becoming an actor. Her mother saw a call for an open audition for Notes on a Scandal (2006), and Juno was successful in winning the role of Cate Blanchett's daughter. This was her big break and led to a role in another high profile film, Atonement (2007). She dyed her hair red to play Lola.
In 2009, Juno moved to Los Angeles, partly to be with her boyfriend and partly for her acting career.
- Whilst studying at Bedales boarding school, she asked her St. Trinian's (2007) co-star Rupert Everett to help her with her drama homework, but she only scored a C-minus.
- From when she was really young, her parents used to take her to the Glastonbury music festival every year.
- Considered for the role of Luna Lovegood on Harry Potter and the Order of the Phoenix (2007), but the role went to Evanna Lynch.