The 30-year-old actress confirmed reports that she gave birth to her first child with her husband, Mumford & Sons frontman Marcus Mumford, during an appearance on The Graham Norton Show. She also revealed that the two welcomed a baby girl!
"It is a girl and she's three weeks old," Mulligan said.
Mulligan is currently promoting her new film, Suffragette, and has impressively already returned to red carpet form. Just last Wednesday, she dazzled in a grey Chanel dress at the movie's premiere during the opening night gala of the BFI London Film Festival.
Mulligan and Mumford have been married since April 2012. The Great Gatsby star's pregnancy was first reported in June.
"I've always wanted to be a mother," she recently told Elle UK. "I love what I do, but I'm excited for this next phase of my life."
In April, Mulligan's good friend, actress Sienna Miller, dished on the Oscar-nominated actress' relationship with her 28-year-old musician husband.
"They both come from very solid families and have a real sense of the life they want to live," Miller told Vogue in April. "They have chickens and a dog, and roasts and friends, jams by campfires. It's sort of idyllic. Marcus can headline Glastonbury and Carey can be nominated for however many Oscars, and then they come back to their farm, and they're in big woolly jumpers and funny hats, raising piglets. It's an amazing balance they've managed to strike. I can't wait for a little baby to come along."
Check out the video below to see another glowing mama -- Ashlee Simpson, who gave birth to her and husband Evan Ross' daughter, Jagger Snow, in August -- looking healthy and incredible just two months after giving birth.