Barty, the first Australian woman into the final of her home Grand Slam since 1980, is looking to add to her 2019 French Open and 2021 Wimbledon titles.
Osaka, winner of the 2019 and 2021 Australian Opens, has vowed to have more fun on court this year, following a difficult last year in which she said she had suffered from depression.
Ash Barty defeats Karolina Pliskova 6-3, 6-7 (4), 6-3 for her second Grand Slam title, which also came on 50th anniversary of fellow Australian Evonne Goolagong Cawley's maiden crown.
World number one Ash Barty successfully defended her Miami Open title, beating Canadian Bianca Andreescu 6-3 4-0.
Sofia Kenin counter-punched her way back from a set down against Garbine Muguruza to win her first Grand Slam title with a 4-6 6-2 6-2 win.
Naomi Osaka has withdrawn from the WTA Finals because of a right shoulder injury ahead of her scheduled round-robin match against top-ranked Ash Barty.
After dominating the first set tiebreak, Barty broke the big-serving Pliskova in a 12-minute game to open the second set.
US Open winner Sloane Stephens and world number one Simona Halep cruised into the final to set up a rematch of the French Open final.
But while the world number one cruised through her quarterfinal clash in straight sets, she made it very clear that she was unhappy playing three matches in two days.
The carnage of seeds at the world's premier grass court tennis tournament continued, with only one of the top 10 women's seeds remaining in the tournament at the fourth round.
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