The exciting news was revealed in a touching black and white shot, which was posted on Olivia's Instagram page.
In the snap, the starlet proudly cradles her pregnant belly as her one-year-old son Otis Sudeikis copies her.
"Matching baby bumps," the 32-year-old star captioned the picture.
Speaking of motherhood, the Tron beauty has described the experience as "humbling and adventurous."
"I've loved every second of it, from the second Otis was born. I love watching him sleep. I mean, every mum loves seeing their kids sleep but I really just enjoy learning from him."
Meanwhile fiance Jason hasn't shied away from the fact he'd love a little brother or sister for Otis.
"My own kid [makes me want more], because I made it with Olivia and that seems like a good cocktail," the 40-year-old funnyman told E! News.
Watch Olivia talk about motherhood in the player below. Post continues after the video!
Last week, Olivia stepped out in New York looking as radiant as ever.
The star concealed her burgeoning belling in a tasseled black dress.
Since welcoming her son Otis with Jason, Olivia has delighted fans with her real and honest posts about parenting.
Last year, she shared a disheveled selfie and joked: "I call this hairstyle, 'keep the kid alive'. Products you'll need: sweat, string cheese, diaper rash cream, chewed up crayon, snot, and an enthusiastic spritz of panic."
Congratulations to the Wilde-Sudeikis clan!