Blanchett, 38, delivered son Ignatius Martin Upton on Sunday in Sydney, said Tim McKeough, media relations manager at the Sydney Theatre Company, where Blanchett and her playwright husband are co-artistic directors.
"All are well and very happy," McKeough said.
The newborn weighed 3.6 kilograms (7.94 pounds), he said.
Blanchett and husband Andrew Upton have two other sons: Dashiell, 6, and Roman, 3.
Australian Prime Minister Kevin Rudd offered his congratulations to the family in a statement Monday, and said Blanchett would still co-chair an arts panel at a national summit on Saturday.
The Australia 2020 summit will gather 1,000 leading Australians to propose ideas for the future direction of the country, with panels including health, climate change, economy and the arts.
The Academy Award-winning actress next appears on-screen with Harrison Ford in the movieIndiana Jones and the Kingdom of the Crystal Skull, due in theatres in May.
