The Australian went into the final day at Royal Queensland Golf Club in Brisbane three clear of Hoshino and mixed five birdies and a spectacular chip-in eagle with four bogeys to seal the win.
He carded 20-under for the tournament, building on a successful year in which he won the Macau Open on the Asian Tour last month and earned 2024 playing rights for the US PGA Tour.
But another victory on the DP World Tour had eluded him until now, having broken through for his first European win at the 2020 Vic Open then claiming the 2021 Scottish Open title.
"It's unbelievable, I've always thought I could win, it took a while to get over the hump," said Lee, whose sister Minjee Lee is the women's world number five.
"But two wins in the last month or so and I'm really proud of my team and myself. I made it interesting for myself early on and through the middle, but I ended up hanging on," added Lee after his triumph in DP World Tour's 2024 season opener.
Six-time Japan Tour winner Hoshino put up a gutsy fight at his first tournament in Australia, hauling in Lee's overnight three-shot advantage by the second hole.
But he couldn't maintain the momentum and ended with a 68 for outright second on a day that saw Chile's Joaquin Niemann, who plays on the Saudi-backed LIV Golf tour, sink a hole-in-one at the par-three fourth.
It was the second ace of the tournament after Australian Curtis Luck did the same at the 17th on Friday.
Niemann carded 67 to finish fifth, two shots behind Luck in fourth. Fellow LIV Golf star Marc Leishman was third after a best-of-the-day 64 left him four strokes behind Lee.
Defending champion and one of LIV Golf's superstars, Cameron Smith, missed the cut.
Lee suffered early nerves, over-hitting his approach at the first to open with a bogey then par, while confident playing partner Hoshino drilled consecutive birdies as the Australian's overnight three-shot lead evaporated.
But Lee kept his cool to restore his three-shot advantage by the sixth after two well-taken birdies following aggressive drives, coupled with a bogey from Hoshino.
A long-range eagle at the par-five ninth gave Lee a four-stroke cushion as pumped the air in celebration to a huge ovation from large galleries.
