People magazine said the latest addition to the McIntyre family is expected in May.
"Barrett and I are so blessed and grateful for the little one on the way," said McIntyre, 37. "We'll have our hands full. Three's the new nine!"
The couple's two other children are Griffin Thomas, 3, and Rhys Edward, 1.
McIntyre is one of nine children. The couple married in August 2003 at New York City's Plaza Hotel.
2014: The Year in Music [PHOTOS]