Ashleigh Barty announces shock retirement from tennis at age 25 and as World No. 1

World No. 1 Ashleigh Barty has made a shock announcement that she will retire from professional tennis at the age of just 25.

The Australian star, who became the first home player to win an Australian Open singles title in 44 years in January, shocked the sporting world on social media on Wednesday as she said she was leaving to "chase other dreams".

Barty shared the news via a video posted on Instagram in which she sat down and chatted with her good friend and retired Australian tennis player Casey Dellacqua about the decision.

"Today is difficult and filled with emotion for me as I announce my retirement from tennis," Barty, who has French Open, Wimbledon and Australian Open titles to her name, said in the conversation.

"I'm so happy and I'm so ready. And I just know at the moment in my heart, for me as a person, this is right.

"I wasn't sure how to share this news with you so I asked my good friend [Dellacqua] to help me.

"I am so thankful for everything this sport has given me and leave feeling proud and fulfilled.

"Thank you to everyone who has supported me along the way, I'll always be grateful for the lifelong memories we created together."

The Queenslander admitted that she had been thinking about retiring “for a long time”.

“That’s the first time I’ve said it out loud, and it’s hard to say,” Barty said about her retirement. “But I am so happy, and I’m so ready, and I just know at the moment in my heart [that] for me as a person, this is right.

“I know I’ve done this before, but in a very different feeling, and I’m so grateful for everything tennis has given me – it’s given me all my dreams plus more.

“There was just a little part of me that wasn’t quite satisfied, wasn’t quite fulfilled,” she said. “And then came the challenge of the Australian Open, and I think that for me just feels like the perfect way, my perfect way to celebrate what an amazing journey my tennis career has been.

“I know how much work it takes to bring the best out of yourself and I’ve said it to my team multiple times, it’s just I don’t have that in me any more,” she said. “I don’t have the physical drive, the emotional want and everything it takes to challenge yourself at the very top of the level any more.

“I just know that I am absolutely – I am spent – I just know physically I have nothing more to give. And that to me is success. I have given absolutely everything I can to this beautiful sport of tennis.”

Barty’s long-time mentor, Evonne Goolagong Cawley, led tributes to her fellow legendary Australian as the surprise decision prompted a flood of warm wishes and congratulations from stars around the sporting world and beyond.

“I’m so supportive of Ash and making a decision that is the best for her and makes her happy,” Goolagong Cawley said.

“I can’t wait to see what the next chapter brings and to watch Ash achieve her dreams.”

Eurosport expert Barbara Schett has said she was not particularly surprised by the Australian's announcement given her life priorities, all she has achieved and the tough travel restrictions.

"Well, to be honest, I was surprised that it happened today, but I'm actually not surprised that she is retiring," Schett told Eurosport.

"I always thought that she was not going to have a very long career. She did not love the game as much as maybe other players have loved it, and she is not driven by success or money or anything like that. So that was a bit of a surprise factor today, and you can imagine what is going on in Australia.

"But at the end of the day, to me, I thought maybe she was going to play at the US Open this year, and then she would call it quits, and she has done it now at the height of her game - and wow, what a champion!

"It is crazy to imagine: I think it is the first time, from my recollection, it is the first time in history that somebody has walked off being a reigning Grand Slam champion and a world No. 1. That is still a big decision, a big move to take, even though you might not have the motivation anymore.

"I'm sure it has been a big decision, but that decision has been in her head for quite some time. She said after she won Wimbledon that she was already thinking, 'oh, should I continue?', and I think especially what she has gone through in the last two years with all the travel restrictions. She has been away from home so much that it has made it even more clear to her that she probably wants to retire sooner rather than later.

"I actually thought when she won the Australian Open and I was sitting quietly that maybe this was the time, maybe she was going to announce it and shock everybody. She did not do it then. She probably needed to digest things a little bit. Think about it: it was awfully quiet after that Australian opening victory. She was not in the media, not in the press. She did not really do anything, and how she came to the decision today, I don't recall anybody on that high of a level, No. 1 in the world, winning two of the last three Grand Slams, as well."