Pratt, 41, confirmed Monday that he and Schwarzenegger, 30, welcomed a daughter, Lyla Maria.
Pratt shared a photo on Instagram of himself and Schwarzenegger holding their baby girl's tiny hand.
"We are beyond thrilled to announce the birth of our daughter, Lyla Maria Schwarzenegger Pratt. We couldn't be happier. Both mom and baby are doing great. We are extremely blessed," he captioned the post.
Pratt also included two bible verses in the caption.
"Psalm 126:3 The LORD has done great things for us, and we are filled with joy," he wrote.
"Psalm 127:3-4 Behold, children are a heritage from the Lord, the fruit of the womb a reward. Like arrows in the hand of a warrior are the children of one's youth. Blessed is the man who fills his quiver with them! He shall not be put to shame when he speaks with his enemies in the gate."
Pratt also has a 7-year-old son, Jack, with his ex-wife, Anna Faris.
Schwarzenegger's brother, actor Patrick Schwarzenegger, also confirmed the baby's birth in a video obtained by Entertainment Tonight on Sunday. Patrick Schwarzenegger was leaving a market in Santa Barbara, Calif.
"They're doing great -- just got her a little gift," he said while showing a package wrapped with a pink ribbon.
A source told ET that Pratt's car was spotted Friday at St. John's Hospital in Santa Monica, Calif. Schwarzenegger's parents, Arnold Schwarzenegger and Maria Shriver, were later seen visiting the couple's home.
Schwarzenegger and Pratt married in June 2019. News broke in April that the couple were expecting.
On Instagram Live in June, Schwarzenegger discussed her experience being pregnant during the coronavirus (COVID-19) pandemic. She said Pratt was being "wonderful" during her pregnancy.
"I'm really lucky to be living in very close proximity to my family, which has been really helpful," Schwarzenegger said. "And then, obviously, I have a wonderful husband who's very, it's been amazing having him home and also very understanding about my need to sanitize everything, have everyone wear masks all the time."
Pratt plays Peter Quill, aka Star-Lord, in the Guardians of the Galaxy movies and Owen Grady in the Jurassic World films. The third Jurassic World film, Jurassic World: Dominion, started filming again in July.