The 26-year-old actress and model – who has bared all on stage with the Calendar Girls tour and competed in I’m A Celebrity… Get Me Out of Here! and Celebrity Masterchef since leaving Hollyoaks in 2006 – will play Tamzin in the rapid response team and will appear on screens in September.
Gemma said: “I am absolutely thrilled to be joining Casualty and really looking forward to getting to know all the cast and crew.
“I used to watch the series as a child so to now be involved is fantastic. I’m so grateful to be given the chance to play Tamzin and I hope audiences will enjoy her, too!”
Gemma will be joined by Dhafer L’Abidine as competitive paramedic Omar.
Tunisian-born actor Dhafer starred alongside Sarah Jessica Parker and Kim Cattrall as Sheikh Mahmud in Sex In The City 2.
Olive Kent, producer of the BBC One medical drama, said: “We are delighted to welcome Gemma and Dhafer to Casualty. Tamzin is going to bring a touch of glamour to the paramedic team and set some hearts racing in the Emergency department while Omar’s melting roadside manner is going to raise the temperatures of Holby’s female patients!”