The 43-year-old funnyman, who will host the Oscars next month, and his veterinary technician wife, 38, welcomed a baby girl in a New York hospital.
The couple, who wed in 2000, have a 19-month-old son, Nathan Thomas.
TV network Comedy Central posted a message on their website, declaring: "Mom, dad, baby and big brother are all doing great."
Stewart's spokesman Matt Labov tells People magazine, "Maggie Rose Stewart was born on Saturday afternoon in Manhattan and she was six pounds, nine ounces."
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