Spears delivered the child via C-section. Federline was with her in the delivery room. No other details were immediately available.
The singer, 23, first announced that she was pregnant in April, saying, "The time has finally come to share our wonderful news that we are expecting our first child together."
On Aug. 6, the singer celebrated her impending motherhood at a Moroccan-themed baby shower at her Malibu home with friends and family, including her mom and sister, as well as Federline's mother and his stepmother.
This is the first child for Spears. Federline has two children, Kori, 3, and Kaleb, 1, from a previous relationship with actress Shar Jackson.