His victory in the 50m Breastroke gave him his second gold for the tournament in Bucharest.
Peaty's time of 25.99 was enough to take the title, with Brazil's Joao Gomes Junior second in 26.52, and South African Cameron Van Der Burgh claiming bronze with a time of 26.60.
“That felt really, really good even though I slightly messed up a stroke.
“There’s definitely more in there somewhere but it will take a lot more hard work to make that happen. We’re only at the start of our four-year journey to Tokyo 2020.”
Peaty now has five golds in the two World Championships that he has so far contested.
Elsewhere, the US broke the world record in the morning heats of the 4x100m Mixed Medley Relay. Britain's team of Georgia Davies, Adam Peaty, James Guy and Siobhan-Marie O’Connor came fifth with a time of 3:41.56. That time would have broken the previous world record, but they had to settle for claiming just the European record.
O'Connor, who swam the anchor leg for Brtain, said:
“I’m gutted I couldn’t get it at the finish but I knew that I’d be hunted down.
“I gave it everything and it’s just disappointing because I wanted to get a medal for the team.
“We’ve got such a strong team but that event is such a tricky, tactical event and I think we’re just still learning it. It’s still a relatively new event in the programme but the team is so strong and I know we’re only going to get better.”
There were more records broken. Max Litchfield set a British and Commonwealth record in the heats of the Men’s 200m Individual Medley, finishing in 1:56.64.
“I had some great messages of support after this morning’s swim, my dad’s out here and I spoke to him but it was a case of switching off from it all and just getting ready for tonight,” said Litchfield.
“The tactic tonight was a case of doing the same thing as this morning and I pretty much did that. It felt good. We’re always trying to move forward and thankfully I can do that by putting the hard work in everyday and it’s paying off for us so I’m happy with that.”
Georgia Davies claimed a British Record as she finished first in her semi-final of the Women’s 50m Backstroke. With a time of 27.49, she qualified in fourth for the final tomorrow.
Duncan Scott had success in the Men's 100m Freestyle semi-final, finishing second.
Scott said after the race:
“There’s no way I can be disappointed with that.
"It’s a nice step forward from this morning which is what I wanted to do.
“Bring on the dog fight tomorrow. It might take a best time to take a medal - there’s some fast guys in there so you never know.”
Italy's Federica Pellegrini became the first swimmer to win seven medals in a single event at the world championships after a stunning victory in the women's 200 metres freestyle final on Wednesday.
Federica Pellegrini sacrée sur 200m nage libre aux Mondiaux de Budapest
Image credit: Getty Images
On a glittering night for Italy, Gabriele Detti won his first world title in a close finish in the men's 800m freestyle, an emotional Chad le Clos of South Africa took gold in the men's 200m butterfly and Britain's Adam Peaty secured a breaststroke double with 50m gold.
Pellegrini last won a world title at the 2011 championships, but the determined Italian rolled back the years to clock one minute 54.73 seconds.
The oldest in the field at 28, Pellegrini stormed back from fourth at the final turn to take gold ahead of Katie Ledecky of America and Australia's Olympic bronze medallist Emma McKeon, who had led until the 150m mark.
In the process Pellegrini, who broke 10 world records before she was 21, scuppered the hopes of silver medallist Ledecky becoming only the second swimmer, after Michael Phelps, to win at least two world titles in four different individual events.
Additional reporting from Reuters.