Queensland swimmer Shayna Jack has capped her comeback from a drug ban by coming second in the women's 100 metres freestyle event at the Australian Swimming Championships in Adelaide.

Her second spot in a personal best time guarantees her selection for the Australian team for the World Championships in Budapest in June and Commonwealth Games in Birmingham in July.

The race was won by Mollie O'Callaghan, who set the fastest time in the world this year of 52.49 seconds.

It is the first time Jack has made an Australian team since she ended her two-year ban for taking a minute amount of the banned drug Ligandrol in 2019.

Jack protested her innocence but, after a series of court challenges, she was forced to sit out the sport and miss last year's Olympic Games.

Jack last competed for Australia at the 2018 Commonwealth Games, where she won a relay gold medal.

"I'm overwhelmed with emotion to be back on the team," said Jack as she fought back tears.

"Not very many people know what I actually really went through – you know the depths of it and to be back and wearing those colours again means more than anything to me.

"My goal was to love swimming and fall in love with it again and I have and I'm really, really proud to be back.

"It's still a journey, I'm still learning and doing things and working with psychologists with all those things and that's been really, really beneficial with my comeback."

Jack's time of 52.60 was the second-fastest time in the world this year behind O'Callaghan.

"To be completely honest I am stronger, and I am fitter and faster than ever, which I just proved, and this is just the beginning for me," she said.

The performance of O'Callaghan and Jack points to the ongoing strength of Australian women's sprinting.

Emma McKeon, who won four gold medals at the Tokyo Olympics, is sitting out these swimming championships as is Kate Campbell, who has won 7 national championships, and her sister Bronte.

But O'Callaghan and Jack as well as Meg Harris who came third and Madison Wilson who came fourth in world-class times, showed that Australia will field a formidable relay team at the World Championships and Commonwealth Games.

"We're a weapon to be scared of and I can't wait to see what we can do best at the Worlds," Jack said.

That team will be strengthened even further when McKeon returns for the Commonwealth Games.

O'Callaghan said she was surprised with her stunning swim — a personal best after setting another personal best during the morning's heats.

"I think it was just more nerves and stuff and I kind of sometimes a little bit doubt myself, but yeah I'm really surprised it was such a big jump," said the 18-year old.

Pop star Cody Simpson joins Dolphins ranks

Pop singer and actor Cody Simpson gave himself a chance of selection for the Australian team at the World Championships by coming third in the Men's 100m Butterfly.

The event was won by Tokyo dual bronze medallist Matthew Temple in 51.50 seconds.

Olympic 100m freestyle gold and silver medallist Kyle Chalmers was second.

Chalmers is returning to swimming after a shoulder operation but has said he won't compete at the World Championships, which opens the door for Simpson's selection.

"To get on a podium at a national meet is pretty unreal," Simpson said after recording 51.96, equalling the FINA qualifying mark.

Simpson returned to his junior sport in 2020 after establishing a stellar career as a singer and actor.

He said making the Australian team would mean everything to him because his mother, Angie, also swam for Australia.

"I was told as a little boy that I'd want to swim for Australia as well and then obviously I was side-tracked for the better part of ten years," he said.

That "side-track" saw him become an international pop star in his teens, gain modelling contracts and perform in a Broadway musical

He said his "other career" as a pop singer was "on the back-burner for now".

"I mean I released an album a few months ago, it's still something that I like to do.

"Ian Thorpe was always telling me, 'if you stop playing music, I'll stop mentoring you'," he said.

Simpson said he talked about returning to swimming with other superstars of the sport including Grant Hackett and Michael Phelps.

"That obviously just gave me the air under my wings to want to give it a crack," Simpson said.

Earlier, Tokyo Olympian Elijah Winnington began his return to swimming redemption by defending his Men's 400m freestyle national title in 3:43.10.

Winnington went into the Olympics as a gold medal favourite but performed disappointingly, finishing seventh.

He said he fell into a state of semi-depression after the Games.

"The last real 400 I did was the one in Tokyo which I kind of walked away from very disappointed as you can imagine," he said.

"It's a race I've been very nervous for coming back, this is my big race really since Tokyo," he said.

He said he's spent a long time working on his psyche since Tokyo.

"I've had months and months of psychological sessions, just reflective sessions and even like really positively trying to reflect on Tokyo and see all the advantages I got from that outcome although it might not have been the result that I wanted," he said.

Rio gold medallist Mack Horton came second behind Winnington, guaranteeing him a spot in the World Championships and Commonwealth Games.

Horton missed out on an individual swim at Tokyo although he was selected as a relay swimmer.

"I can say that I'm still growing and still learning," Winnington said.