The actress will start work at the ITV1 drama again next month, reprising the role of Ashley Thomas's ex-wife Bernice Blackstock.
Giles, confirming her comeback, told the Daily Star Sunday: "It's so lovely to be asked back to Emmerdale. The show is on top form and I'm really looking forward to being part of the team again."
Meanwhile, Emmerdale's series producer Stuart Blackburn told the newspaper: "Bernice Blackstock has always been one of Emmerdale's most popular characters. Linked to Nicola, Ashley, Diane, Rodney and her daughter Gabby, she remains right at the heart of the show.
"With the recent separation of Ashley and Laurel, and problems ahead for Diane, the time is right for Bernice to come back and really stir things up."
Bernice originally appeared on Emmerdale between 1998 and 2002, memorably having an affair with chef Carlos Diaz during her marriage to Ashley. She later made a brief return in 2004.