British sports performance director Chelsea Warr stepped down just six months before the 2020 Tokyo Olympics.
The Australian will join the Queensland Academy of Sport as chief executive officer later this year.
Warr, who joined UK Sport in 2005, was a key figure behind Britain’s successes in London 2012 and Rio 2016.
In December, he claimed that Britain could break their medal record from Rio to Tokyo, after finishing second in the ranking in 2016 with 67 medals.
“We would like to thank Chelsea Warr for the significant contribution she has made to the British Olympic and Paralympic sport in the past 18 years; both in the United Kingdom sport and before that of British swimming,” UK Sport said in a statement.
“We wish you every success in your new role in your home country.”
UK Sport said Deputy Performance Director Michael Bourne took over on a provisional basis to “ensure continued support for our performance team and sports as they complete preparations for Tokyo.”
The body, which allocates funds for the Olympic and Paralympic sports, added that it will start looking for Warr’s replacement.
BBC sports editor Dan Roan
Considered Warr’s reputation as one of the key figures behind Britain’s extraordinary appearance as a true Olympic and Paralympic center in recent games, and his role as leader of the country’s high performance system, the timing of this announcement, just six months before Team GB made their way to Tokyo, it will stun many in British sport.
With much of the preparation already done and Warr is unable to take on his new role in Australia until after the Games, the impact on Team GB’s fortunes in Japan should be minimal.
But he has also driven performance plans for the next eight years, and there will be concern that he is now going to a direct competitor.