The 24-year-old led home Great Britain team-mate James Wilby in a time of 57.14 seconds with Yan Zibei of China in third.
His winning time meant there was no new world record for Peaty, who had shattered his own world mark with 56.88secs in the semi-finals on Sunday.
And it was also marginally slower than his previous world best of 57.10, which he had set at last year’s European Championships in Glasgow.
But it was still more than enough to ensure his third-consecutive world title at the distance, well over a second in front of Wilby, who recorded a time of 58.46 in second place.
Wilby’s silver marked his first world medal, and something of a surprise one after he had qualified in third place from the semi-finals behind Zibei.
Peaty’s dominance in the event stretches back to 2015 when he broke the world record for the first time at the British Championships, his time of 57.92 making him the first man to go under 58 seconds.
Nevertheless Peaty professed bigger ambitions, insisting it was possible to lower the target by at least another second, and launching his ‘Project 56’ campaign.
Peaty achieved that target in style in the semi-finals and – although he did not lower it further in the final – he has maintained it could be possible to go faster still.