"We feel so lucky to have been able to experience the miracle of birth once again and are forever grateful for the opportunity to be the parents of another little angel. Vivian Lake was born at home on December 5. She is healthy and full of life," Bundchen wrote Friday on Facebook.
"Thank you all for your support and well wishes. We wish you and your families many blessings."
The couple has a son, Benjamin, who turns 3 on Saturday.
Brady also has a 5-year-old son, John, with actress Bridget Moynahan.
The birth of Vivian comes during a big week of preparation for Brady, who will lead New England (9-3) into a Monday night showdown against the AFC leading Houston Texans (11-1) with home-field advantage in the playoffs still up for grabs.