Pratt took to Instagram on Monday to announce the birth of their daughter, Lyla Maria Schwarzenegger Pratt.
"We couldn’t be happier," Pratt wrote in an Instagram post with a photo of himself and Schwarzenegger holding the baby's hand. "Both mom and baby are doing great. We are extremely blessed."
USA TODAY has reached out to the couple's reps for further comment.
Schwarzenegger's younger brother Patrick, 26, confirmed the couple had welcomed their first baby together in a video obtained by Entertainment Tonight.
"They're doing great, just got her a little gift," he told a reporter in a Santa Barbara, California, parking lot on Sunday while holding up a package wrapped in a pink bow when asked how mom and baby were doing.
He also said "thank you" when congratulated on becoming an uncle – Katherine, the oldest of the Schwarzenegger children, is the first to welcome a child. Pratt shares 7-year-old son Jack with his ex-wife, Anna Faris.
On Aug. 1, Pratt, 41, gave a shout-out on his Instagram story to Schwarzenegger, 30, who hiked with him to the top of a mountain despite being so far along in her pregnancy.
"Ready to pop, still don't stop," the "Jurassic World" star wrote, along with a picture of his wife and her prodigious baby bump. "Kinda grateful it didn't go down on the trail tho to be real."
“She has changed my life for the better in so many ways,” Pratt told E!’s "In the Room."
He added that Schwarzenegger has already been a great stepmom and that his heart, soul and son are safe with her.
“She’s, God willing, going to be a great mom one day," he continued. "She’s got great parents, great siblings. She fills in all my many deficits.”
Schwarzenegger, the eldest child of former California Gov. Arnold Schwarzenegger and ex-wife Maria Shriver, opened up to "Entertainment Tonight" on July 9 about how she and Pratt were occupying themselves while preparing for the arrival of their newborn.
"I think No. 1, just surrounding yourself with your loved ones, in a safe way, obviously, has been nice," she said. "
She added that much of the fun of her quarantine life has taken place in the kitchen, which keeps her "calm in this crazy time."
"It was my New Year's resolution to get more comfortable in the kitchen with cooking. I've always loved baking, but I definitely wanted to learn more in the cooking department. And to learn non-intimidating and simple recipes."
During his appearance on "The Tonight Show Starring Jimmy Fallon" in May, Schwarzenegger's father, Arnold, marveled at the genes of his future grandchild, whose maternal grandmother is a member of the Kennedy family.
"The Kennedy, the Schwarzenegger and Pratt, I mean, we can do anything," he said with a grin. "We can go and solve the Cuban Missile Crisis. We can go and kill predators with our bare hands, and we go and training the dinosaurs. I mean think about it. That is a lot of the power here.”
Contributing: Hannah Yasharoff, Jenna Ryu, Morgan Hines
This article originally appeared on USA TODAY: Katherine Schwarzenegger, Chris Pratt welcome daughter Lyla