The 28-year-old known as "The Missile" hung up his goggles on Wednesday only three weeks after visiting Singleton.

He had 15 major event medals to his credit.

"Throughout my whole career I have no regrets about anything inside the pool or out," he told reporters in Sydney.

"Everything has shaped the person I am today. It's almost scary to think if I had won that gold medal I wouldn't be who I am now.

"It's made me a much more humbled, relaxed and easy going person, I believe."

Growing up in Port Macquarie on NSW's mid north coast, Magnussen said even the thought of competing in the Olympics felt like a wild dream.

"A silver medal at the Olympic games was something I never could have dreamt about and I achieved it," he said.

"Reflecting on it now, it's something I'm actually quite proud of."

Magnussen took his silver in the men's 100m freestyle in London, touching just behind American Nathan Adrian, and won the men's 100m freestyle at the 2011 and 2013 World Championships.

The 28-year-old regards both world titles as career highlights but particularly the first.

"I went in as a big underdog and nobody knew my name. I think that's the first time I got the nickname 'The Missile'," he said.

He also won 100m freestyle gold at the 2014 Glasgow Commonwealth Games and was a member of Australia's champion Commonwealth 4x100m freestyle relay team in 2010, 2014 and 2018.

Last year's Commonwealth Games had felt like like a swansong with friends and family poolside - some for the first time, he said.

Magnussen said he spent 18 months thinking about retirement as it became more difficult to maintain his love for the sport because of injury.

He suffered recurring shoulder issues in recent years and underwent surgery in 2015.

"I feel I could have swum at another Olympic Games but with the lofty standards I have held myself to over the years and the high expectations I have, I believe now is the right time to step away from the sport," he said.

"I have always been proud to stand on the starting blocks representing my family, my friends and my country. There is no greater honour or responsibility."

He's confident about Australia's Olympic prospects next year in Tokyo and is hoping to get to Japan to watch.

"It's going to feel really weird not being there with them," he said.

"Hopefully they'll miss not having me as part of the team too, as much for out of the pool comedic relief as in the pool results."

Swimming Australia President John Bertrand said Magnussen should be very proud of scaling heights in competitive sport achieved by very few.

Australian Associated Press