Manaudou became a national heroine at the 2004 Athens Olympics at age 17 when she took gold in the 400 metres freestyle.
She also won silver in the 800m freestyle and bronze in the 100m backstroke.
Despite going on to set several world records and win three world titles, Manaudou struggled to stay on top as problems with her long-time coach and an ugly breakup with her Italian swimmer boyfriend saw her picture splashed over the gossip magazines and the internet.
She said: "It's decided.
"It wasn't an easy decision to take.
"It wasn't an impulsive decision.
"I realised at this moment that swimming was no longer a pleasure for me."
As Adlington swept to victory in the 400m and 800m freestyle failed miserably and fled the pool in tears.
After starting strongly and holding the lead at the half-way point of the 400m, she ended up finishing last, admitting giving up during the race after struggling to keep up with Adlington.
Manaudou, who is also reported by friends as being pregnant, ended her 2009 season in January saying she had lost the will to compete at the highest level.
She said: "The hunger hasn't come back.
"Today I have other interests ... I just know that when I get up in the morning I don't feel like going to swim.
"I have all the titles.
"I have all that I wanted, even more than I dreamed of.
"I have plenty of time to think about my future."
Manaudou is one of France's biggest female sports stars and has several lucrative sponsorship deals.
"There's also the media pressure.
"Whatever I do, I am always spied upon.
"I hope that they will leave me in peace."
Manaudou claimed she also regretted her decision to abandon traditional schooling at the age of 14 to carry on her swimming and advised any future swimming stars to carry on with their studies.
She said: "All my life I've talked swimming.
"When I come across someone who's not involved in it, I don't have many things to say.
"And I'm shy.
"They [up and coming swimmers] should live their passion but not stop their studies.
"It's important to build oneself up, to get away and to think of other things.
"Personally, I would have preferred to have something alongside swimming."
The news was met with disappointment from France national coach Christian Donze, who automatically thought ahead to the next Olympic Games in London in three years' time.
He said: "With such a talent I was convinced that she could get herself back in the saddle for 2012."