The Australian had been suspended for four years after a sample she provided in an out-of-competition test in June 2019 was found to have contained ligandrol.

Having appealed the ban at the CAS, Jack has instead been ruled out of the sport for two years and her ban backdated to July 12 2019, the date her provisional suspension came into force.

The CAS confirmed she had committed an anti-doping rule violation but the sole arbitrator found she "did not intentionally ingest ligandrol and considered that she had discharged her onus of proving that the anti-doping rule violation was not intentional."

Jack, who had claimed cross-contamination could have caused her positive drugs test for the non-steroid anabolic agent, responded to the ruling with a statement posted on social media. 

"The anti-doping rules are far from satisfactory and can produce results that are far from fair," she said. 

"In my case, I have proven that I have NOT ever cheated, nor used prohibited substances intentionally or knowingly. 

"I will still incur two years out of the sport in which I love.  

"I cannot change the rules and the rules will remain as they are for the time being. 

"Therefore, I accept this decision with a positive attitude and with gratitude that my career as a swimmer will resume next year.  

"I have never doubted myself for a minute throughout this ordeal and I have never allowed my integrity to be compromised.  

"I walk a little taller tonight with the fact that this ordeal is finally over.  

"I am returning to swimming – the sport that I have loved all my life and the sport that I will cherish just that little bit more ongoing."

The 22-year-old, a member of Australia's 4x100 metres freestyle team that won gold at the Gold Coast 2018 Commonwealth Games in a world record time, has been a vocal critic of the anti-doping system, which she claims is "flawed".

Her compatriot and teammate Cate Campbell also criticised the anti-doping system following the CAS verdict, claiming Jack had been viewed as guilty until she could prove otherwise.  

"There’s a fine line between a hard stance on drugs, which of course we want, then taking it too far to where the athlete really suffers," Campbell said, as reported by The Sydney Morning Herald. 

"And I think we haven’t got the balance quite right.

"This case and the cases that have come forward, even since Shayna return her positive test, have shown that there is probably good window of opportunity to have a discussion, make it really robust and make sure that athletes are protected, in every sense; protected from anti-doping but they also work in a system that helps protect them as well and give them the best opportunity to compete.

"Shayna couldn’t even go and join her local netball team. 

"That is a really important part of sport… she’s had the entire sporting community ripped away from her. 

"In the criminal system, you’re innocent until proven guilty. 

"Anti-doping works the other way around, you are guilty and it’s up to you to prove your degree of guilt. 

"There is something flawed in that."

United States Anti-Doping Agency chief executive Travis Tygart, who has previously criticised the World Anti-Doping Agency (WADA) as part of a long-running dispute between the organisations, did so again following the CAS verdict on Jack. 

"To treat athletes in those circumstances just the same as you would an intentional cheat, particularly if there is no performance enhancing by a single positive test at those low levels, it is simply a system that can't sustain itself," he said.

International Olympic Committee member and WADA Executive Board member Dick Pound has been more bullish about the verdict, however, claiming that Jack is still a "doped athlete". 

"Your athlete was not innocent — it was a doped athlete, it was a doping offence," Pound said, as reported by ABC. 

"The only argument was the length of the sanction? 

"She got that reduced because the CAS panel determined there was no significant fault.

"I don't know what evidence they heard to overturn the four-year part, as opposed to two years, but that's what courts are for... the sentence of the guilty person is reduced, but the person is still guilty."

Jack's positive test was returned prior to last year's World Championships in South Korea and led to her being sent home from Australia's pre-competition training camp in Japan.

Her suspension will expire less than two weeks before the start of the postponed Tokyo 2020 Olympic Games, due to open on July 23 2021.