A representative for The Devil Wears Prada star confirmed the couple's happy news to Usmagazine.com.
The stars married in Italy in 2010, and Blunt, 30, has long been open about her desire to start a family.
She recently said of her plans to have kids, "We want to have children; I just don't know when yet. I'm just not sure about the timing of all of that. We're both from big families, so I think it's something we want."