"I'll be showing soon," the 48-year-old said. "Daniel and I are so happy. We're going to have a little human. We can't wait to meet him or her. It's all such a mystery."
Weisz and Craig, 50, married in 2011, after a whirlwind six-month courtship. Both have a child from a previous relationship. Weisz has an 11-year-old son, Henry, with director Darren Aronofsky; Craig has a 25-year-old daughter, Ella, with actress Fiona Loudon.
Weisz was talking to the New York Times about her new movie, "Disobedience," which opens April 27. But aside from her surprising revelation, the actress tends to keep mum about their relationship.
"He's just too famous," she has previously said. "It would be a betrayal. You have to protect your marriage."
Craig, of course, is famous as the current James Bond. He'll reprise his role as 007 in the franchise's next movie, slated for Nov. 8, 2019. It might be the last time, though; Craig often talks about stepping away. And the British bookies love placing bets on who might play Bond next.
One person not in the running? Craig's wife. She doesn't think Bond should be played by a woman.
"Why not create your own story rather than jumping on to the shoulders and being compared to all those other male predecessors?" she said. "Women are really fascinating and interesting and should get their own stories."