The actor, who plays advertising ace Harry Crane in the show, and his wife Virginia welcomed a son, Patrick Ryan Sommer, in Los Angeles.
The tot weighed in at 7 pounds, 9 ounces (3.4 kilograms) - and Sommer has now told how thrilled he is with the family's latest addition.
He tells People.com, "We are loving hanging with our happy, healthy baby boy, and appreciate our family and friends joining us in celebrating this exciting time. Also, he looks way better than I do in a onesie."
The couple already has a daughter, two-year-old Beatrice.
MAD MEN star RICH SOMMERS is a new dad - the actor's wife VIRGINIA gave birth to the couple's son on Tuesday night (31Aug10). Sommers, who plays Harry Crane in the hit drama, and his wife will call the baby Patrick Ryan Sommer.