Opposition Leader Tony Abbott says the birth of the Duke and Duchess of Cambridge's son would be the happiest day of their lives.
He and wife Margie sent their congratulations and best wishes to Prince William and wife Catherine on the birth.
The long-time monarchist expects all Australians would share their joy in the birth of the new prince, who is third in line to the throne.
"While there will come a time to contemplate the constitutional duties that await the young prince, today we simply welcome a baby boy into the world and share the joy of this young family," Mr Abbott said in a statement.
"I am sure that over the course of his life, the prince will, like the rest of his family, develop a deep affection for our country, as we already have for him."
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Australian Greens leader Christine Milne added her congratulations while citing the minor party's Republican leanings.
"As staunch Republicans we still have great affection for the royal family and wish them well," she told reporters in Canberra.
"But (we) hope of course that we will be a republic long before the new baby ever becomes king."
