The 41-year-old "Avengers" actor and the 30-year-old children's book author announced the birth of daughter Lyla Maria Schwarzenegger Pratt in a joint post on their Instagram accounts Monday.
The post included a photo of the hands of both parents and child and a pair of Bible verses; including Psalm 126:3: "The Lord has done great things for us, and we are filled with joy."
Pratt also has a 7-year-old son with his first wife, Anna Faris.
The baby is the granddaughter of Arnold Schwarzenegger and Maria Shriver.