After setting two world records on Tuesday's third day when qualifying 0.73 seconds clear of the field, Peaty was expected to touch first by some margin at the Duna Arena on the banks of the Danube.
And the 22-year-old Uttoxeter swimmer did not disappoint, clocking 25.99 seconds, just 0.04secs down on his own world record, which he had been evens to break with Sky Bet. His victory margin was 0.53secs.
Silver went to Joao Gomes of Brazil in 26.52 and bronze to Cameron van der Burgh of South Africa in 26.60.
Peaty's world record coming into the championships was 26.42, set in winning gold in Kazan, Russia two years ago.
His heat swim on Tuesday lowered the mark to 26.10 and he knocked a further 0.15 off it in Tuesday evening's semi-final to take it to 25.95.
Peaty won 100m gold on Monday with the second quickest time ever - behind only his Olympic gold medal-winning swim - and now has replicated his individual haul from the 2015 World Championships.
Peaty experienced disappointment to go with earlier elation as he returned for the 4x100m mixed medley relay just over 60 minutes later.
Peaty swam the second breaststroke leg, after Georgia Davies on backstroke and before James Guy on butterfly and Siobhan O'Connor on freestyle as Britain finished fifth behind the United States.
Britain had qualified fourth fastest, behind Australia, Canada and the United States, who improved the world record Britain set in Kazan, Russia to three minutes 40.28 seconds in the morning heats.
The mixed medley relay was recently added to the Olympic programme for the Tokyo 2020 Games and the USA, Australia and Britain sent in their leading swimmers for the final at the Duna Arena.
Britain finished in 3mins 41.56secs as the USA team of Matt Grevers, Lilly King, Caeleb Dressel and Simone Manuel took gold in a new world record of 3:38.56.
Australia's Mitchell Larkin, Daniel Cave, Emma McKeon and Bronte Campbell took silver in 3:41.21, while Canada and China tied for third place in 3:41.25.
Peaty told the BBC: "It's quite exhausting coming in and coming out, switching off and switching on, especially tonight when I had the double, but I'm so, so happy with my performances here.
"These last four days have been very, very hard work.
"I've been on a rollercoaster of emotions - world records at the top and then trying to get myself grounded for the next race.
"I'm over the moon with my performances - 57.4, the second fastest in history. It gives me confidence that I can one day go 56.
"That dream now is burning more alive than ever."
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