"It's just I don't have that in me anymore. I don't have the physical drive, the emotional want and kind of everything it takes to challenge yourself at the very top level anymore.
"I think I just know that I'm absolutely, I am spent. I just know physically I had nothing more to give and that for me is success."
One of the most respected and loved players on tour, Barty also became the best -- with her dizzying array of slices, pinpoint serving and seamless forehand typifying her all-round game.
Few athletes can boast such a varied sporting resume as the down-to-earth Australian.
She began playing tennis as a child in the Queensland state capital Brisbane and went on to win the junior Wimbledon title as a 15-year-old in 2011.
But the expectations that came with success took their toll and she made a shock decision three years later to ditch tennis for cricket, signing for Brisbane Heat in the inaugural Women's Big Bash League.
Dream comes true
But the lure of tennis was never far away and she returned after a season out, breaking through for her maiden Grand Slam triumph at the French Open in 2019 and becoming Australia's first women's world number one since Evonne Goolagong-Cawley 50 years ago.
Barty finally won a cherished Wimbledon crown last year before her Australian Open triumph at Melbourne Park in January, storming back from 5-1 down in the second set against American Danielle Collins to triumph 6-3, 7-6 (7/2).
"It's something I've been thinking about for a long time," she said of retirement.
"To be able to win Wimbledon, which was my dream, the one true dream that I wanted in tennis, that really changed my perspective. And I just had that gut feeling after Wimbledon and had spoken to my team quite a lot about it.
"And there was just a little part of me that wasn't quite satisfied, wasn't quite fulfilled. And then came the challenge of the Australian Open and I think that for me just feels like the most perfect way."
The Women's Tennis Association praised Barty as "an incredible ambassador for the sport".
"For every young girl that has looked up to you. For every one of us that you've inspired. For your love of the game, thank you, @ashbarty, for the incredible mark you've left on-court, off-court and in our hearts," the WTA said.
Australian prime minister Scott Morrison also paid tribute.
"I do want to say thank you, Ash, for inspiring a country, inspiring a nation, at a time when this country really needed a good shot in the arm," he said.
Barty has been world number one for more than two years and said after her Australian Open win that she wanted time to consider her next move, withdrawing from the prestigious early season hardcourt tournaments at Indian Wells and Miami.
Late last year she became engaged to long-term boyfriend Garry Kissick, who was ever-present courtside when she played and often posted supportive messages on social media.