Australian pop singer-turned-swimmer Cody Simpson qualified for this year's Commonwealth Games after finishing third in the 100 metres butterfly final at the national trials in Adelaide on Wednesday.

Simpson, 25, turned heads earlier on Wednesday when he upstaged Olympic freestyle gold medallist Kyle Chalmers and won his heat in a personal best time of 51.79 seconds behind defending champion Matt Temple (51.64).

Temple clocked 51.50 in the final while Chalmers, who won 100m freestyle gold in Rio and silver in Tokyo, also improved to 51.67.

Simpson's 51.96 matched governing body FINA's A qualifying time for next month's world championships in Budapest.

With Chalmers not attending the event, Simpson is on track for a remarkable world championships debut, according to local media reports.

"I didn't even think I’d be remotely competitive until this year at the earliest, so to make the team is just a bonus on the way to Paris," Simpson told Amazon.

The top three in the final under the A time qualify for the July 28-Aug. 8 Commonwealth Games in Birmingham, England.

Simpson, a talented junior swimmer before pursuing a music career in his teens, finished eighth in the 100 butterfly final at Australia's Olympic trials last year to fall short of a place in the Tokyo team.

Twice Olympic 1,500m freestyle champion Grant Hackett tipped a big meeting in Adelaide for Simpson before the trials.

"I actually think Cody’s a real chance," said TV pundit Hackett.

"He's done all the work. He looks super fit and the body’s in good shape."

Shayna Jack returned from a doping ban to finish second, behind Mollie O'Callaghan, in the women's 100 metres freestyle final to secure a place in the Australia team for the world championships and Commonwealth Games.