The mark, if nowhere near the 21-year-old's own world record of 57.92 that he set at the same national championships last year, was faster than August's world championship-winning time of 58.52.
"Just qualified for my first Olympic Games, no other feeling like competing for your country at this level," he said on Twitter.
Despite being a big hope for gold, Peaty said he had taken nothing for granted despite being world champion at the distance.
"The pressure is off now, which is great," he told the British Swimming website.
"I know that wasn't near my best, I'm glad that I came first but I know what went wrong and what went well in that race. Hopefully next time I can get out a bit faster and come back stronger."
Peaty won world championship titles in the 100 and 50 breaststroke in Kazan, Russia last year as well as the 4x100 mixed medley relay and is hoping to become the first male British swimmer to capture Olympic gold in 28 years.
The relay and 50 are not in the Olympic programme but Peaty is also aiming for the 200 breaststroke, a distance he has not swum since January. That trial event is on Friday.
Double world champion James Guy dominated in the 400 freestyle final by clocking three minutes 43.84, also well inside the Olympic consideration time.
"The pressure is off now and I can enjoy the rest of the meet," he said. "I know I can make little improvements now ahead of the summer."
Hannah Miley, a 400 women's individual medley silver medallist at the 2011 Shanghai championships, won her event in 4:33.40 which should also see her safely on the plane to Rio in August for her third Games.
British swimmers won only three medals, a silver for Michael Jamieson in the 200 breaststroke and freestyle bronzes for now-retired Rebecca Adlington, at their home Games in London in 2012 but are hoping to strike gold in Rio.
The British team is due to be announced next week.
(Reporting by Alan Baldwin, editing by Tony Jimenez)
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