But how did the Australian teenager motivate herself to beat one of the greatest swimmers of all time?
As part of the new Bridgestone Olympic Channel experience Olympic State of Mind, Titmus reveals the sports psychology tools she uses to stay ahead of the competition.
The goal of Olympic State of Mind is to help people live their best lives, through applying the principles of motivation, visualisation, and mindfulness.
There are interviews with elite sports stars and medical professionals, informative articles, quizzes and interactive games.
Motivated by career goals
Titmus is known as "Arnie" or "The Terminator" by her team-mates, which is fitting given her relentless attitude to be the best.
"Motivating myself for training is always super easy because I always have my goals," the Tasmanian-born swimmer told Olympic Channel.
"I try to keep them in the front of my mind and I try to do a lot of self-talk, and repeat them. I remember the positive things I've done in previous races.
"If I have a bad race, the biggest motivation for myself is to look at where it went wrong and then try and fix that.
"I'm motivated by the things I want to achieve in my career. Most people understand that you can't achieve if you don't put the work in." - Ariarne Titmus to Olympic Channel
Rock and roll playlist
Another tactic Titmus uses to focuses her mind before training and racing is listening to music.
This mindfulness helps her to stay in the present moment and not be distracted by other swimmers.
"Before every race I play the same playlist," she told Olympic Channel.
"It's my mum's playlist and she's a massive head-banger, and it's all rock. The beat really gets me into the mood i need to be able to race." - Ariarne Titmus to Olympic Channel.
"Music not only gets me in the zone, but I use it to separate myself from other people and make sure I don't talk to anyone else, and really focus."
In Titmus' quest for a gold at Tokyo 2020, she draws inspiration from a triple Olympic champion.
"My favourite quote is from Stephanie Rice, who came to visit Tasmania when I was younger.
"I went to get my T-shirt signed by her, and she wrote, 'Be the best you can be.' I suppose you could say that's my mantra."
Titmus then describes how anyone could apply this mantra to their daily lives.
"Getting up in the morning and going to the gym in order to live a healthy lifestyle is something that people have to motivate themselves to do.
"If you want to look a certain way or fit in a certain dress it's literally the same thing. Tell yourself you can do it and you can do it."
"If you have the right will and drive then it's the same as me wanting to push hard in the pool, for them to get to the gym and make sure they're healthy."
How to tap into Ariarne Titmus' Olympic state of mind
The interactive experience is now live on Olympic Channel.
Keep an eye out for the video clips, articles, quizzes and games for you to watch, read, and play, plus a special episode of the Olympic Channel Podcast.