The mom of two posted three photos from her family's time at the hospital, with the snaps featuring Underwood, her husband, Mike Fisher, and their older son, 3-year-old Isaiah.
The first shot was of Underwood holding her newborn to her chest as she looked at the camera, with baby Jacob sleeping peacefully while wearing a tiny hat.
Next, the Oklahoma native posted a shot of Fisher holding his younger son, with the former NHL player smiling at the camera as he cradled the wrapped-up infant.
The third photo saw Isaiah holding his new brother with some assistance from his dad, with the 3-year-old looking stylish in a fedora as he gazed at his sibling.
"Jacob Bryan Fisher entered the world in the wee hours of the morning on Monday...his mom, dad and big brother couldn't be happier for God to trust them with taking care of this little miracle! Our hearts are full, our eyes are tired and our lives are forever changed," Underwood captioned the snaps. "Life is good."
In May, baby Jacob will join his mom on her Cry Pretty Tour 360 along with big brother Isaiah, something Underwood admitted will be a bit of a challenge.
"It's going to be a different ball game, for sure," she told the Tennessean. "My brain, I'm such a planner. I want to know how it's all going to go. But no matter who you are, you make it happen, you make it work, you get your team behind you."
Isaiah is already a touring vet, having traveled with his mom on her Storyteller Tour back in 2016 when he was just over a year-old.
Jacob isn't the only new member of the family to arrive in recent days, as Fisher used Instagram on Jan. 19 to share that they had brought home another dog, who became the family's third canine companion after joining pups Ace and Penny.
"Meet the newest member of our family!" Fisher wrote alongside a snap of an adorable German Shepherd dog. "Isaiah affectionately named him Zero. I guess it fits because it's the chance of surviving if you try to break into our home."
Photo Credit: Twitter / @carrieunderwood