Osaka also won the 2020 U.S. Open, giving her back-to-back major titles for the second time. She pulled off the same feat in the 2018 U.S. Open and 2019 Australian Open.
The 23-year-old Japanese sensation held the advantage over Brady in almost every major statistical category in the championship match, including winners (16-15), aces (6-2) and break points converted (4-2).
Brady was making her first appearance in a Grand Slam final.
The first set came right down to the wire after they traded breaks in the middle of the set.
Brady twice held a two-point edge (30-0 and 40-15) while serving at 4-5, but she couldn't close out the critical game as Osaka came back to secure the break and the first set.
The second set was less dramatic as the No. 3 seed stormed out to a 4-0 lead on the strength of two breaks and cruised to her second Australian Open title.
It wasn't the cleanest match as the players combined for more unforced errors (55) than winners (31), but it was Osaka's play on the key points that put her over the top.
She's now 4-0 in major tournament finals, and she's happy the latest one came with fans in the stands after capturing the U.S. Open without spectators amid the coronavirus pandemic.
"I didn't play my last Grand Slam with fans so just to have this energy it means a lot," Osaka said during the trophy presentation. "Thank you so much for coming. I feel like playing a Grand Slam is a super privilege right now and it's something I won't take for granted. Thank you for this opportunity."
Meanwhile, Brady is on the ascent, with two straight Grand Slam events where she at least reached the semifinals. She'd never previously advanced beyond the fourth round before last year's U.S. Open.
"Tonight it wasn't meant to be," she told reporters. "Hopefully there's many more."
In the bigger picture, it feels like Osaka has now established herself as the player to beat on tennis' biggest stages, especially considering her semifinal victory over Serena Williams, who held that unofficial title for around two decades.
Next up on the Grand Slam schedule is the French Open, which is slated to start May 23 at Stade Roland Garros in Paris.