The 25-year-old said she wanted to be eligible in time under international drug-testing protocols to represent her country again at next year's World Championships in Shanghai.
The former 50 and 100 metres freestyle world record holder retired last December, claiming she wanted to move on to the next stage of her life.
But Trickett said she started to realise in recent months that she still felt the need to compete and she had already resumed light training with her coach Grant Stoelwinder.
"I think it really solidified it at Pan Pacs [Pan Pacific event in California last month] seeing the guys race," Trickett said on television.
"I guess I was just ready to test myself again and really I just want to see how far I can take my swimming and see how fast I can get."
Trickett refused to wear high-tech body suits, a stance which is held to have cost her a title at last year's World Championships in Rome.
The controversial polyurethane suits have now been banned, which Stoelwinder said would benefit her as she returns to competition.
But Leigh Nugent, Australia's head coach, said that while he was delighted that Trickett was back he was unsure whether she will be able to return to her best.
It could take a year until it was clear whether she could recapture the form that won her three gold medals at the 2008 Beijing Olympics in the 100m butterfly and the 100m freestyle and medley relays, he said.
"I wouldn't be making any predictions about whether I was confident or not, we'll just watch her progress and maybe in 12 months' time I could say whether I'm confident or not," Nugent said.
December 2009: Trickett to miss London 2012 after retiring at 24
November 2009: Trickett will make decision on London 2012 next month