Peaty confirmed 12 months ago he wanted to push for a place at the next Games, shortly after it was announced that the 50m breaststroke event would be added to the schedule.
It gives the Briton a further opportunity to win individual golds, having done so in the 100m in 2016 and 2021.
Meanwhile, double Olympic champion Duncan Scott, 28, held off a strong challenge from Edward Mildred to win the 200m butterfly.
Lauren Cox, who won 100m backstroke gold at the 2025 European Championships, finished clear of Blythe Kinsman to win the same discipline in London.
Three-time Paralympic champion Alice Tai had to settle for second, finishing behind Bethany Firth, in the women’s MC 100m backstroke.
Other winners included 17-year-old Amelie Blocksidge in the 1500m freestyle, Max Litchfield in the 400m medley and Amalie Smith, 16, in the 400m medley.
British titles will be awarded in 36 medal events across the meet in London this week.
