"Tom and Katie are very excited, and the entire family is very excited," says DeVette.
In June, Cruise proposed to Holmes atop the Eiffel Tower in Paris. Asked by PEOPLE at the time if the couple planned to have children, Holmes paused and then said, "Yes," as both she and Cruise broke into smiles.
DeVette says no wedding date has been set and would not comment on the baby's gender or say how far along the pregnancy is. The rep did say that Holmes, 26, "has never felt better."
Cruise, 43, is currently shooting Mission: Impossible 3 in Los Angeles.
More on Tom & Katie
The star, who in the past had been protective of his personal life, openly smooched his new sweetie and told reporters: "She is an extraordinary woman." Later he grabbed a TV camera with both hands, stepped in front to assure a good close-up of his grin and said, "Do you see the smile on my face?"
Cruise's enthusiasm for Holmes, who became a TV star on the teen drama Dawson's Creek, continued with a memorable appearance on The Oprah Winfrey Show when he jumped on her couch and declared his love for Holmes.
Though some questioned the sincerity of the relationship, DeVette told PEOPLE in June: "When he's happy and he has something to share he wants other people to share in the happiness."