Maguire is best known for playing the title role in the trilogy of "Spider-Man" blockbusters. His spouse designs jewelry.
"Tobey and Jen are thrilled," a source close to the couple told Usmagazine.com. "They can't wait to expand their family with another little one."
The Maguires, who married in September 2007, are already the parents of 2-year-old Ruby Sweetheart.