The 22-year-old was the aggressor against Polish fifth seed Magdalena Frech, who absorbed that power to claim her maiden WTA title 7-6 (7-5) 6-4.
The Paris Olympian's run from qualifying included the scalps of 2017 US Open champion Sloane Stephens, former Australian Open finalist Danielle Collins and Italy's former top-20 talent Martina Trevisan.
Her efforts will see her ranking soar 64 spots, from No.152 up to a new career-high of 88, importantly putting her in the box seat for automatic qualification at January's Australian Open.
Gadecki, whose previous high mark was No.120 in the world, will also jump six compatriots to become the country's top women's player.
"This is quite humbling; massive congrats to Magdalena; you played very well," Gadecki said.
"You (the crowd) made me feel the love and I'm so happy I've been able to play my first final here.
"Thank you to my family back home for supporting me and my team in London staying up all night to watch me, I really appreciate it."
Frech, 26, will rise to No.32 in the world with her first title.
"Dreams do come true," she said before heaping praise on the Australian.
"Let's keep going, let's win more."
The first Australian in a WTA 500-level final since Ash Barty in 2022, Gadecki defied pressure on her serve and took the first set to a tie-break.
Superb touch at the net pushed Gadecki within sight of the first set but, up 5-4, another brutal forehand just sailed wide and the Pole seized her moment to take the set.
Gadecki wasn't fussed, swinging cleanly to claim the first break of the match and lead the second set 2-0.
But she was broken twice, the Australian then saving a match point and breaking back in a gritty ninth game, only to cough up another service break and surrender the match.
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