Manners, who played Bex Reynolds in the BBC One hospital drama, will join the cast as area car driver Kirsty Knight from February.
Her character will be involved in a storyline alongside Sgt Callum Stone (Sam Callis).
"Kirsty is a lively addition to the team. She has an irreverent sense of humour and a love of the adrenaline-fuelled side of the job," producer Tim Key told The Sun.
The 34-year-old's TV credits include Doctors, Holby City and Mile High. She also took part in the 2004 series of Strictly Come Dancing, where she partnered Brendan Cole.
Earlier this week, ex-Hollyoaks star Barry Sloane, former EastEnders actress Kara Tointon and Torchwood's Gareth David-Lloyd were also confirmed to make appearances in the ITV1 show.