Cooper, 28, revealed the exciting news on Instagram on Tuesday.
"Scarlett and I have been blessed with wonderful news we are ecstatic to share," he wrote. "This summer we will be welcoming a new member to the family.
"The two of us could not be happier as we wait for the arrival of our little one," Cooper added.
Cooper also shared a photo of Byrne, 29, sitting with her hands placed right below her baby bump, as well as a short video of the couple walking hand-in-hand on the beach.
Scarlett also took to her own social media account to share the news, writing: "Cooper and I are delighted to share that we have a little one on the way. Our hearts are filled with gratitude and joy, and the two of us can’t wait to meet the newest little Hefner."
The actress, who starred as Pansy Parkinson in the "Harry Potter" franchise, shared the same photo as Cooper, as well as another sweet snapshot of the couple.
Cooper and Scarlett married in November 2019.