Beth Mooney top-scored with 74* as the world's top-ranked team posted 156/6, and a brilliant bowling display saw South Africa stifled in their chase, with the Proteas falling short of their target.
Their victory means Australia have now won six Women's T20 World Cup titles, and they have completed a 'three-peat' under the captaincy of Meg Lanning, winning in 2018, 2020 and now 2023.
Tasked with defending a target of 157, Australia's bowlers throttled the scoring rate of South Africa's openers at the start of the reply, conceding just 22 runs in the Powerplay and with in-form Tazmin Brits sent back to the dugout by the electric Darcie Brown.
Australia Fend off Laura Wolvaardt Threat
A Darcie Brown catch saw Marizanne Kapp dismissed for a run-a-ball 11 off Ash Gardner as South Africa struggled to up the scoring rate, with 105 runs still required at drinks with ten overs remaining.
The brilliance of Laura Wolvaardt threatened to bring South Africa back into the game as she hit big shot after big shot to surge to 61 from 48 balls.
But Megan Schutt removed Wolvaardt and Jess Jonassen cleaned up the dangerous Chloe Tryon (25 from 23) as the required rate of scoring proved too much for South Africa in the death overs.
And Australia saw it out comfortably in the end, winning by 19 runs to add yet more silverware to the team's bulging trophy cabinet.