The 36-year-old actress will appear as the flirty Fiona Lynch in the next series of the hit ITV drama.
She said in a statement: "I am absolutely thrilled to be joining the cast of Wild at Heart in Africa.
"Fiona Lynch is certainly a fun and feisty character and will no doubt cause quite a few headaches for [husband] Ed and Danny. I can't wait!"
Robert Bathurst, best known for his recurring role as widower Sir Anthony Strallan, was cast as Fiona's husband Ed Lynch in July earlier this year.
Halfpenny has previously starred in EastEnders as Kate Mitchell and Waterloo Road as Izzie Redpath.
Wild at Heart is expected to return to ITV1 in its usual Sunday evening slot for its seventh run from January.