"Thank you Jesus for this amazing blessing. Ladies and Gentlemen, I introduce to you my son. Maverick Pierce James. The best gift for the Christmas season that I could ever ask for," he captioned the photo.
The country star, 35, didn't give any more information about the birth of his son, and has typically maintained his privacy even as he has become a music star.
Fans do know he married his wife, Kelli James, in 2014 and that Maverick has a big sister Lexi who was born in early 2016, but not much else is known about his family.
Regardless, many were thrilled to see the new addition to the James family. "What a beautiful photo of a beautiful baby," one fan commented.
"Congratulations to you, your lovely wife and your lovely daughter on the new love in your lives. Blessed. Love his name."
"Oh wow! Didn't know you were having another baby! A bounty of blessings!" another added.
James finished third in season nine of American Idol, and put out a new album, Strip It Down, in June.