Moffett will appear as Briony who is sent to Emergency Department after being injured in a football fight.
The actress said: “I’m thrilled to be working on the British institution that is Casualty. Being in Cardiff and working for the BBC is, as always, a privilege.”
Costa will play her fiancé Matthew who suffers burns from a flare set off by a teenager.
The pair’s episode will air in October and start a plot line commemorating the centenary of the start of WW1 which producers say will conclude in spin-off show, Holby.
Oliver Kent, Executive Producer, commented: ‘Both Antony and Georgia are a welcome addition to the new series of Casualty – they have a fantastic energy and were great fun to work with. I’m sure audiences will love them together onscreen!’
