She began her career as a child actress in the BBC One drama The Chase (2006–2007), the CBBC series Grange Hill (2007–2008), and the ITV soap opera Emmerdale (2009–2012).
She is the older sister of actress Raffey Cassidy, who portrayed Athena in Tomorrowland.
[3] Cassidy's most notable role so far is that of Rachel Towers in BBC children's drama Grange Hill, but she has had a number of smaller roles in multiple television series of the past few years, including The Street, The Chase and Marian, Again.
Cassidy also had a guest spot in Casualty 1909, spin-off of the drama series Casualty, appearing in this occasion alongside her real-life brother Mossie Cassidy in his first TV role.
Cassidy portrayed Matty Barton in Emmerdale prior to his transition when still going by "Hannah", with her first appearance in the soap being 17 July 2009.