It was revealed on February 2, 2006 that Lynch, who was then fourteen, had been cast as Luna Lovegood in Harry Potter and the Order of the Phoenix after her father flew her to London for the open audition for the role,^[7] beating nearly 15,000 girls in the auditions.^[3] However, as Lynch has naturally dark blonde hair, her hair had to be bleached light blonde for the role of Luna. On set Lynch became very good friends with fellow actresses Bonnie Wright (who plays Ginny Weasley), Katie Leung (Cho Chang) and Afshan Azad (who plays Padma Patil).

Since the release of the film, she has received many positive reviews, being called one of the true "standouts" of the film