Schwarzenegger turned 31 on Sunday.
"Happy Birthday Sweetie! You have brought so much light into my life," Pratt wrote on Instagram alongside a collage of photos of his wife. "I’m so glad to be home with you and Lyla. You’re a great mom, a great step-mom, a great wife, daughter, sister and friend. The world is brighter with you in it. I am one lucky man. Thank you for the love, support and partnership. I love you."
Pratt and Schwarzenegger welcomed Lyla together in August, while Pratt is also dad to 8-year-old son Jack from his previous marriage to Anna Faris.
In a candid post on Instagram on Friday, Schwarzenegger opened up about how pregnancy and motherhood have been "challenging" amid the coronavirus pandemic. However, she also looked at celebrating her daughter's first Christmas as a "silver lining."
"While this Holiday season will look different for us all, this little ornament my sister Christina got us, and the experience of our daughters first Christmas is a big silver lining of joy and light for me," Schwarzenegger wrote. "2020 has been a crazy year, it’s not what any of us expected; it’s been filled with a lot of challenging times and unpredictable twists and turns. It has also been a year of immense joy for those of us who have welcomed life into the world. Being pregnant in a pandemic and having a baby too, was not how I expected my pregnancy and becoming a mother to go, but i couldn’t be more thrilled and grateful to have my little Lyla Maria in my life and to be able to be her mom."
"Shout out to all the people who had babies this year, became pregnant, are pregnant, or are trying to get pregnant," she added. "It’s a wild time to embark on this journey of motherhood and I see you! 🙏."
A source tells ET that Pratt and Schwarzenegger will celebrate Christmas with an "intimate group" this year.
"Chris and Katherine have been enjoying time with their daughter Lyla. It’s only been a few months but the couple has a great routine down and things have gotten better now that Chris is home from filming in London," the source shares. "The family will spend the holidays together with a more intimate group and has really been enjoying their time together. With the pandemic happening it hasn’t been a traditional birth and time to enjoy it with family and friends but the couple is doing what they can while staying safe."
See more on Schwarzenegger in the video below.