Campbell’s first lead role came in 2009 playing Lucy in online drama Freak.
She won the 2014 BAFTA TV Award for Best Actress for her role as Ashley Jones in Murdered by My Boyfriend. Since 2014 Campbell has starred in the Sky 1 comedy drama After Hours and the TV mini-series Tripped, as well as playing a supporting role in BBC drama One of Us and in 2016 appeared in Channel 4 series Flowers. In 2017, she appeared in the ITV series Broadchurch as DC Katie Harford and in the Black Mirror season 4 episode "Hang the DJ". In 2018, she began playing Lyta-Zod in Syfy drama Krypton.