England chased down a target of 128 with one over to spare to wrap up the series and ensure Australia's women suffered the same fate as their male counterparts.
Australia captain Jodie Fields admitted her world champions were shattered after being desperate to make amends for the men's 3-0 series loss.
"I'm pretty gutted to be honest to be sitting here and have lost the Ashes," Fields said.
"Particularly after the men lost, we saw it as our responsibility to work hard to bring it home and now both Australian teams have gone home without the Ashes."
England's victory was set up by a superb innings by Lydia Greenway, whose 80 not out was the highest score by an English woman in T20.
The win gave the hosts an unassailable 10-4 lead in the points-based, multi-format series with one match to play, a final Twenty 20 in Durham on Saturday.
Australia lost the title they won in 2010-11 but will get a chance to make amends in another Ashes series during the Australian summer.
"I suppose all we can do is go away now and have a good hard look at ourselves as a team and look at what we can improve on," Fields said.
"I'm sure you'll see a fighting team in the January series."
After the only Test match of the series was drawn, Australia took the early advantage by winning the first of one-day matches.
However England turned the tables with four straight wins.
In a match played as a curtain raiser to the opening men's Twenty20 clash on Thursday, Australia needed a bright bowling start after being kept to a modest 7-127 from 20 overs after winning the toss.
And they got it, with three wickets inside the first three overs.
Julie Hunter (1-23) struck first, bowling Heather Knight for two before Sarah Coyte (2-29) dismissed Sarah Taylor and Danielle Wyatt inside three balls to have England 3-9.
However Charlotte Edwards (24) and Greenway steadied the ship with an impressive 67-run partnership and they got home on the back of the Greenway's stellar innings.
Earlier, opener Meg Lanning top-scored with 60 for Australia.
Dual international Ellyse Perry scored 11 runs and had 0-21 from three overs with the ball to continue a modest series by her standards.