The actor and his wife, Rachel, welcomed their first child on Tuesday, July 28, confirming the newborn's name to People.com as Bear Maxwell Sullivan.
The new dad also shared the announcement on Instagram, posting a close-up shot of the baby's feet.
"HE HAS ARRIVED!", Sullivan captioned the sweet snap. "8lbs of beautiful baby boy."
"Witnessing @therealrachelsullivan bring our first son into this world, after 20 hours of labor, was one of the great honors of my life. It was primal and intentional and I have never been more in love with this powerful woman.
"She and baby are resting and recovering well. Everyone is healthy and exhausted."