"Wanted to let the news out directly. Emily and I are so incredibly happy to welcome our daughter Hazel into the world today! Happy bday!" the new dad tweeted on Sunday.
The adorable lovebirds announced that they were expecting their first child together in September 2013.
The Into the Woods actress and The Office actor tied the knot in Italy in 2010 after dating for two years.
The 30-year-old British beauty celebrated Hazel's impending arrival and gathered with close friends and family at a star-studded baby shower on Dec. 15. Jennifer Aniston, Justin Theroux, Kristen Bell and more famous faces joined the expecting parents at a private residence in Los Angeles.
Blunt had been, well, blunt about her desire to become a mother in previous interviews. Speaking to Manhattan magazine in 2012, she said, "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."
Congrats to the new family!