The 37-year-old announced the happy news on Thursday, February 14 night, taking to Instagram to share a photo of his partner, Megan Coughlin, holding the newborn to her chest.
The couple's four-year-old daughter, Charlie, can also be seen in the touching image.
"Momma bear," he captioned the post.
Winchester had only just shared the exciting news Coughlan was expecting earlier in the day, posting a photo of the then-mum-to-be in a hospital gown with the caption: "Game Time! #baby2 #strongmomma #soon."