The couple welcomed their third child together in Austin, Texas, on Friday, sources confirm to PEOPLE.
The pair, who are also parents to Vida, who turns 3 next month, and Levi, 4, announced the pregnancy just one month after their June nuptials in Texas.
Camila, 29, joked that even as she put on pregnancy pounds, her actor husband, 43, was losing weight – dramatically – for The Dallas Buyers Club, in which he plays the real-life Ron Woodruff, who contracted HIV.
"We have gone the complete opposite direction eating wise, but we're navigating it," she said last summer. "But I don't really have cravings yet."
McConaughey's latest movie, Mud, will be released April. 26,