The couple, who confirmed their relationship in June 2016, both shared the news on Twitter.
“After much speculation I’m overjoyed to announce that [we] are expecting our first child.#blessed,” they both wrote.
A source told The Sun: “Sophie and Shayne have been keeping the exciting news to themselves to enjoy the moment in private.
“But mum and baby are doing amazing and they’ve started telling their nearest and dearest.
“It’s definitely shocked a few people because of how fast it’s happened, but they’re completely in love and are excited about becoming first-time parents.”
Austin, who played Lindsey Butterfield in Hollyoaks, announced in March 2016 that she had split from her husband Graeme Rooney.