The 32-year-old mother of two, who plays barmaid Michelle Connor in the Weatherfield soap, is due to continue working throughout her pregnancy and will depart on maternity leave in early summer.
Speaking of the news, the couple said: "We are delighted to be able to announce that we are having a baby. All our family and friends are very excited at the prospect of a new arrival next summer."
In March, it was announced that she and husband Jack Ryder were to end their six-year marriage.
Four months later, Kym and Jamie went public with their relationship at the launch of this year's Inside Soap Awards. Since the announcement, it has been speculated that the pair are engaged to be married.
Kym has two children - David, 13 and Emily, 10 - while, Jamie, who plays Warren Fox in Hollyoaks, has a two-year-old son called Billy with his former girlfriend, Hayley Lever.
Julia Haworth (Claire Peacock), Ryan Thomas (Jason Grimshaw) and Andrew Whyment (Kirk Sutherland) have all become parents in the past six months, while Alison King (Carla Gordon), Wanda Opalinska (Wiki Dankowska), Jane Danson (Leanne Battersby) and Jack P. Shepherd (David Platt) are all expecting new arrivals in early 2009.