The 33-year-old had a boy, Knox Leon, and a girl, Vivienne Marcheline, by Caesarean section on Saturday evening, according to her doctor.
Actor Brad Pitt, the twins' father, was by her side in the delivery room.
"He was perfectly calm and everything went well," Dr Michel Sussmann told reporters. "The parents and the babies are in excellent health."
Dr Sussman said the birth had been moved forward "for medical reasons" but did not give further details.