Hilty, who has been seen on Broadway in Wicked and 9 to 5, gave birth to a girl, Viola Philomena, Sept. 18 in New York City.
Gallagher, who was seen in the recent Broadway revival of Jekyll & Hyde, added on his Twitter account, "Yup! Working on a new project w/ @meganhilty! It's been in development for months now, & is due in September! Working title: #GallagherBaby!"
The couple wed Nov. 2, 2013, in Las Vegas.