"The couple ... are overjoyed with this news and they look forward to welcoming this newest addition into their family," the "Die Hard" star's representative said in a statement confirming Heming's pregnancy.
The baby, the couple's first child together, is due early in 2012.
Willis, 56, married Heming, 35, in 2009. He has three daughters with his ex-wife, actress Demi Moore, the youngest of whom is 17 years-old.
Willis shot to fame in the 1980s on the hit television series "Moonlighting," and went on to become a top box office star in such films as "Pulp Fiction," "The Sixth Sense" and "Armageddon," in addition to the "Die Hard" series.