Sisto and his wife Addie Lane, who married in 2009, welcomed a baby boy into their family on Friday, March 9.
Sisto confirmed the news on his Twitter page, saying: "Unnamed boy is healthy as is mum. Thanks for your wishes."
The Suburgatory star also joked: "Don't tell my wife I had two glasses of wine while she had an epidural."
Sisto and Lane announced in December that they were expecting a baby.
The couple already have a 2-year-old daughter, Charlie Ballerina.