Published Sunday, 30 December 2012
The movie star's wife Camila Alves gave birth to son Livingston, a sibling for their two kids, Levi, four, and two-year-old Vida.
McConaughey announced the pregnancy news in a Twitter post in July, a month after he and Alves wed, and he returned to the site on Saturday to tell fans about the family's new arrival.
In a post, he writes: "Camila gave birth to our third child yesterday morning.
"Our son, Livingston Alves McConaughey was born at 7:43am on 12.28.12. He greeted the world at 9lbs. and 21 inches. Bless up and thank you for your well wishes. Happy New year, and just keep livin, Camila and Matthew McConaughey."