Passey graduated from The BridgeDrama School in London. Passey first started her career in the BBCdocumentary filmThe Last Flight to Kuwait in 2007 opposite Freddie Stroma. Later in 2011, she starred in the British drama film, A Landscape of Lies, written and directed by Paul Knight, and stars Andrea McLean, Lucinda Rhodes-Flaherty and Daniel Peacock. In 2012, she starred in Saint Dracula 3D, written and directed by Rupesh Paul, and stars Mitch Powell and Ciara Bailey. In 2014, Passey starred in The Smoke directed by Ben Pickering, and stars Matt Di Angelo, Lili Bordán, Stephen Marcus and Alan Ford. For her role, Passey stated that she was worried on "how Hollyoaks fans would react to her role" as "it’s one of those things, it’s a sex scene in a film and you can’t have sex without being naked". The film was released on 20 October 2014. On 21 November 2012, Passey started playing the role of Sienna Blake in the Channel 4 soap opera Hollyoaks. Emily Lawrence was initially cast in the role, before Passey replaced her. Tina Campbell of the Metro praised Passey's portrayal and described Sienna as having various layers to her personality. She noted that a backstory consisting ofa woman beating father, unhinged mother and long-lost brother left her normality doomed. She added that "despite her flaws, you can’t help but love Sienna" and deemed her Hollyoaks best character. Katie Archer of BT described Sienna as appearing "sweet and innocent", but "on the inside, things are far uglier." MSN.com labeled the character a "barmaid psychopath". Viewers' perception of Sienna changed during her tenure. A startled Passey told an Inside Soap reporter that Sienna gained sympathy following revelations about her long-lost daughter. For her role as Sienna, Passey won the "Villain of the Year" award at The British Soap Awards 2014. She was nominated for "Most Popular Newcomer" at the 2014 National Television Awards. Passey was nominated for "Best Bitch" and "Best Storyline" in the 2013 Inside Soap Awards. In 2017, she was nominated for "Best Actress" at the British Soap Awards.
