A representative for the couple has shared the news with People.com although specific details about the child's arrival have not been released.
"Katharine McPhee and David Foster have welcomed a healthy baby boy," the spokesperson said.
"Mom, Dad and son are all doing wonderfully."
The baby is the pair's first child together, and Foster's first son, having fathered five daughters from previous relationships.
The happy news emerges a day after McPhee appeared in a pre-taped interview on the "Women on Top" podcast, in which she revealed she was expecting a boy.
"Now that I am having a boy, there are different things I need to worry about to teach him versus the things I would be thinking about with a girl," she told hosts Roxy Manning and Tammin Sursok. "But it's kind of refreshing because I feel like I don't need to think about those societal 'this is the way you look.' I think men have different issues and different things to worry about."
McPhee and Foster wed in London in 2019.
Katharine McPhee's pregnancy was revealed in October 2020 after the 36-year-old star stepped out with a huge baby bump.
71-year-old David Foster is already a father-of-five to daughters Allison, Amy, Sara, Erin, and Jordan, who range in age from 50 to 34.
The couple reportedly had been trying to have a baby since their nuptials. Two of his daughters Erin and Sara Foster made it clear that they fully supported the pair to have a child.