Camila Alves, the 29-year-old model wife of the 43-year-old actor, gave birth on the morning of December 28 at a hospital in Texas, reported TMZ Online.
Information about the sex and name of the newborn have not been disclosed yet.
McConaughey first tweeted about Alves' pregnancy in July, a month after their wedding.
The couple had been dating since 2006 and already have two kids-- Levi (4) and Vida (2).