Justin, 33, shared the happy news on Instagram alongside a sweet black and white photo of his wife nuzzling their new bundle of joy.
"HE. IS. HERE!" the proud dad wrote. "Our little Maxwell Roland-Samuel Baldoni came into this world on Wednesday and showed us that it was possible for our hearts to double in size ...again. We want to thank everyone for all the love and prayers. We are so grateful. So much more to come."
The happy couple are also parents to their 2-year-old daughter Maiya. When the pair revealed the gender of their second child on video, Justin was visibly moved to tears, and he posted a heartfelt letter to his future son on Instagram.
"Dear son, this was such a massively profound moment for us… and clearly it hit me hard," he wrote. "But that's ok, it’s nothing to be embarrassed about… in fact emotions are to be celebrated! Tears are good! It’s hard to explain, but I feel like my entire life has been about getting ready for this experience and yet at the same time I feel completely inept and not ready to be a dad again. I’ve learned so much and made so many mistakes and I continue to make them…EVERY DAY!"
The star also stated he hopes to teach his son that "part of being a man is embracing the parts of yourself that you might be ashamed or embarrassed of. And that eventually, the side of us that we want to hide from the world will be the side that our future life partner will love more than anything."
"I want you to know that while confidence might be important for success, humility is necessary for happiness," he continued. "I hope to show you over the course of your life, to not only respect women, but to stand up, and empower them in both large and small ways. When no one is watching and there's no reward. To be a true friend to train your eyes like a superpower to see women as humans with souls before you see them as objects."
"I can’t wait for you to see this one day and see all the reasons why your daddy was so excited you were going to be born into this crazy, dark, complicated world to a family that is going to love the s**t out of you," Baldoni concluded in his letter. "I might not know you yet little guy, but I am already madly in love with you. I can’t wait to meet you and just know that I am only a few inches away and I’m praying for you every day."
For more on the happy family, watch the video below.