The Games debutants will represent Australia on the world's biggest sporting stage after finishing top two in back-to-back finals and achieving all-important qualifying times.

Harkin, a former Maitland schoolgirl now based in Brisbane, produced a personal best of two minutes, 23.59 seconds (2:23.59) in the women's 200 metre breaststroke.

The 23-year-old, who claimed a national title in the same event in April, was runner-up to Jenna Strauch (2:23.12). The qualifier was 2:24.18.

"I'm so thrilled. It doesn't feel real right now. I had a bit of a tough start to the week, but, oh my gosh, I don't even know what to say," Harkin told official broadcasters Amazon Prime post race.

"It was obviously a massive dream of mine. To be standing here right now next to Jenna, two other breaststrokers already on the team [for the 100m], it's huge. I'm so happy right now."

Hollard followed suit in the next race, winning the men's 200m backstroke decider and stopping the clock at 1:56.44.

The 24-year-old, now located on the Gold Coast after being born in Newcastle and raised in Maitland, was almost one second under the qualifier (1:57.26) and narrowly outside his PB (1:56.40) from an Aussie title two months ago.

"I've got no words," Hollard told official broadcasters Amazon Prime post race.

"The last two trials we were so close and then this one just all came together. I had a back injury and at the end of last year I didn't even know if I was going to be here or not."

Hollard paid tribute to coach Glenn Baker.

"It means everything. Thanks to Glenn Baker over the last five years. I remember in 2016 I called him and he said 'what do you want to do?'. I said 'I want to be an Olympian'."

Emma McKeon (52.35s) edged out Cate Campbell (52.59s) in the women's 100m freestyle final.

Meanwhile, Merewether's Meg Bailey missed qualification for Tokyo after finishing fourth in the women's 200m butterfly final on Tuesday night.