The in-form 27-year-old hit a run-a-ball 102 in Friday's third ODI in Hobart after coming to the crease with the green and gold wobbling at 4-59.
Gardner stabilised with Beth Mooney (50) before Tahlia McGrath (55 from 45 balls) and an unbeaten 12-ball 38 from Georgia Wareham pushed Australia to 8-308.
England's chase showed moments of promise, before they lost 6-22 to be bowled out for 222 in the 43rd over.
Gardner's ton was the first for Australia by an Indigenous woman and the first from a batter at No.6 in the history of female ODI cricket.
"I've played a lot of international games and haven't quite made that mark," she said.
"To be able to reach that was pretty emotional. It was pretty cool to tick off."
MAIDEN TON!!— cricket.com.au (@cricketcomau) Ash Gardner brings up three figures for Australia for the first time, what a knock! #Ashes #AUSvENG pic.twitter.com/fC3zeyQjy6January 17, 2025
Gardner, a Muruwari woman, said she was able to draw inspiration from tattoos of her tribal name and the Aboriginal flag on her arms.
"Whenever I step out on the field I'm playing for more than just myself. I'm playing for my people, my family, my community," she said.
"Having the Aboriginal flag on my front (batting) arm is one of those reminders that there is more to cricket than cricket."
England opener Tammy Beaumont (54) and allrounder Nat Sciver-Brunt (61) combined for an 89-run stand after the loss of two early wickets.
But Wareham, playing her first match of the series, struck crucial blows with her leg spin in the middle overs to remove the pair in quick succession.
Phoebe Litchfield pulled off a stunning diving catch off Alana King in the 37th over to get rid of the dangerous Danni Wyatt-Hodge (35).
King ran through the tail to claim 5-46 after starring with 4-25 in the second ODI.
Australia, who hold the Ashes, have a six-points-to-zero lead in the multi-format series after winning all three ODIs.
They need to reach eight points to retain the silverware, with attention turning to Monday's first of three T20s which are all worth two points.
Alana King has bagged five wickets as Australia beat England in the third ODI of the Ashes series. (Linda Higginson/AAP PHOTOS)
The series concludes with a four-point day-night Test at the MCG.
Gardner, who played a key hand in the first ODI with an unbeaten 42, surpassed her previous ODI top score of 74, struck against New Zealand in December.
She kicked on after combining for a 95-run partnership with Mooney, who was out with almost 18 overs left when she skied a Charlie Dean delivery.
Gardner also had a moment of brilliance in the field when she navigated the boundary rope and threw the ball back to complete a catch.
England skipper Heather Knight said Australia had handled the key moments better.
"We haven't been able to seize the moment and really hammer down any advantage we have got," she said.
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