McKeon won 14 Olympic medals, six of them gold, over the Rio, Tokyo and Paris Games this summer.
"Today I am officially retiring from competitive swimming," she said on Instagram, along with a collage of clips showcasing her many career highlights.
"Leading into Paris I knew it would be my last Olympics and the months since have given me time to reflect on my journey and think about what I wanted my future to look like in swimming," she said.
It was at the Covid-delayed Tokyo Games in 2021 that McKeon really made her name, winning an unsurpassed seven medals to join the all-time swimming greats.
Her four gold and three bronze bettered the six won by East German Kristin Otto (1952) and American Natalie Coughlin (2008).
It also matched the record for most decorated woman athlete at a single Games, tied with Russian gymnast Maria Gorokhovskaya (1952).
A versatile and tenacious freestyle and butterfly racer, her career had looked in jeopardy after failing to qualify for the London 2012 Olympic team.
Instead, she went on to become her country's most honoured Olympian -- a field with plenty of competition given Australia's swimming prowess.
"I am proud of myself for giving my swimming career absolutely everything, both physically and mentally," she said on Monday.
"I wanted to see what I was capable of -- and I did."
Born in Wollongong in New South Wales, McKeon, whose excellence was matched by her humility, had heritage in the pool with her father Ron swimming at the 1980 and 1984 Olympics.
McKeon's mother Susie swam at the 1982 Commonwealth Games while her brother David competed at the 2012 and 2016 Olympics, with Emma and David becoming the first brother and sister to swim for Australia at the same Games in 56 years.
"She was and will continue to be a great role model for younger athletes," said Australian swim team head coach Rohan Taylor.
"She always carried herself with dignity and while we all saw her grace the public can not truly appreciate how tough she is.
"Emma is a fierce competitor and she pushed herself through so many challenges during her career."
Australia's Olympic Committee hailed her for consistently "setting the standard for excellence" while Swimming Australia said he would remembered in the same vein as greats like Dawn Fraser and Ian Thorpe.
"She will also be remembered for how she represented swimming," said Swimming Australia chief Rob Woodhouse, McKeon's uncle.
"The standards she set in and out of the water were second to none and she has a lifelong love of the sport so she won't be disappearing from swimming."
