Bundchen, 32, announced on Facebook that she gave birth to daughter Vivian Lake on Wednesday and even shared an image of the baby's hand, reported E! online.
"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," the supermodel wrote.
"Vivian Lake was born at home on December 5. She is healthy and full of life. Thank you all for your support and well wishes. We wish you and your families many blessings," she added.
Bundchen and Brady were coy about publicly discussing the pregnancy, but it became known that she was expecting a baby in July when she was photographed with a baby bump.
The couple are also parents to son Benjamin Rein Brady, who was born in December 2009.
Brady's wedding to Bundchen was held mere months before Benjamin's birth.