The Oscar-winning actress gave birth on Saturday at the Cedars Sinai Hospital in Los Angeles, where other celebrities like Kim Kardashian and Jessica Simpson have also delivered.
This is the second child for Halle, who already has a five-year-old daughter Nahla from her previous relationship with Canadian model Gabriel Aubry.
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The 47-year-old star, who married her French beau in July in the middle of her pregnancy, has previously said that becoming a mother again was "the biggest surprise" of her life.
"I thought I was kind of past the point where this could be a reality for me," Halle told CNN. "So it's been a big surprise and the most wonderful."
Halle has also revealed that her daughter Nahla has desperately wanted to become a big sister.
"Every night, we do our prayers... She says, 'God, please bring me a bunk bed and a baby sister.' And I say, 'I can do one of those things, I know for sure. The other one, we've got to keep praying on'," said the star.
The news of Halle's pregnancy was confirmed last April, and a few months later Olivier let slip that the couple were expecting a son.
The handsome actor has never married before, but has been romantically linked to actress Mira Sorvino, singer Kylie Minogue and British model Rosie Huntington-Whiteley.
Halle has walked down the aisle twice before, in 1992 when she married baseball player David Justice and in 2001 when she tied the knot with American soul singer Eric Benét.
Several years later, in 2008, Halle and Gabriel welcomed their daughter, although the couple went their separate ways in April 2010.