Osaka, 23, swept past America’s Brady 6-4, 6-3 in 77 minutes to win her second straight major crown and extend a 21-match winning streak that stretches back more than a year.
The world number three, who will rise to second in the rankings, becomes only the third player after Monica Seles and Roger Federer to win her first four major finals.
By clinching back-to-back majors for the second time, the reigning US Open champion has won half of the Slams she has contested since her breakthrough 2018 US Open victory against Serena Williams.
After a tight first set, Osaka controlled the second to win 6-4, 6-3 in 77 minutes in front of 7,381 fans at Rod Laver Arena, operating at half-capacity over coronavirus concerns.
“During my pre-season I would look at the Australian Open trophy from the time before and I would really feel inspired to try to win another one,” she revealed.
Osaka, who did not play last year’s French Open, saved match points against Garbine Muguruza in the fourth round and beat her idol Serena Williams in straight sets in the semi-finals.
But Osaka, a third-round loser in Melbourne last year, said she didn’t expect her charmed run to go on forever.
“I don’t expect to win all my matches this year,” she said. “Somebody can give me a medal if I win all my matches this year, but I don’t think it’s possible.
“I do remember what it feels like to lose a match, very vividly. I remember it here, and I remember how I was feeling and what my mindset was.
“Honestly, it still makes me said to this day, so it’s quite a lingering memory.”
After subduing 22nd seed Brady, a fellow big-hitter, Osaka lifted her racquet above her head in a muted celebration as the crowd roared.
“We played in the semis of the US Open a couple of months ago and I told everyone that you’re going to be a problem,” Osaka told Brady at the trophy presentation. “And I was right.”
The Japanese survived a seesaw start to gain control, reeling off six straight games en route to the title.
It was a rematch of last year’s epic, three-set US Open semi-final, described by some as the best match of 2020, but Osaka triumphed far more comfortably on this occasion.
Before the match, Osaka had pinpointed her own return as the key, but she was helped out by a shaky Brady who lost her serve in the fourth game after two double faults.
But Brady, the 22nd seed, hit back with a break and she continued to pile pressure on Osaka’s serve.
A brilliant lob winner, showcasing her trademark athleticism, gave a pumped-up Brady a break point in the ninth game, but Osaka held on.
Brady then played a sloppy game on serve to hand over the set to Osaka, who had a 20-0 record at Melbourne Park when winning the first set.
Osaka gained a stranglehold with an early break in the second set and fired down an ace to skip out to a 3-0 lead, followed by a roar of “C’mon!”.
Brady attempted a late rally, but a calm Osaka was not to be denied.
Brady’s resilient run ended after serving 14 days’ hard quarantine before the tournament, unlike other players who were allowed out of their hotel rooms to train.
Despite the defeat, Brady will rise to a career-high 13th in the WTA rankings.
Asked what makes Osaka special, she said: “She’s just brings out her best in the big moments.
“But I don’t think, you know, she’s God,” added Brady. “I think maybe Serena is. Maybe she’ll get there, I don’t know.”