The Black Swan actress and fiancé Benjamin Millepied welcomed a baby boy, reports People.
No further details - including the name of the child - have yet been released.
Portman announced her pregnancy and engagement to Millepied in December 2010, though she later confessed that she found it hard to prepare for the baby as she is extremely superstitious.
The Oscar-winnng actress recently revealed that she quit her vegan diet and went back to being a vegetarian upon learning that she was expecting in order to cater to food cravings that she experienced.
Portman has said that she will retire from acting at a young age in order to fully dedicate her time to raising a family.
Along with Millepied, she also spoke out in support of same sex marriage this week as the couple joined Freedom To Marry's Say, 'I Do' campaign.
Watch the trailer for Your Highness starring Natalie Portman below: