She clocked 50.68 seconds, beating her previous record of 51.41, which she set at the US Championships last month.
McLaughlin raced past her competitors to take an early lead, beating Dutch runner Femke Bol and former world champion Dalilah Muhammad, who took silver and bronze respectively in 52.27 and 53.13.
McLaughlin’s supreme performance marked a record run for the American over the past year.
She ran an astonishing 51.90 seconds in the 400m hurdles at the US Olympic trials last summer, according to the World Athletics website.
McLaughlin then set another world record and won gold with a run of 51.46 seconds at the Tokyo 2020 Olympics.
‘Faster and faster’
McLaughlin became the first woman to complete the 400m hurdles in under 51 seconds.
“The weather is absolutely amazing and the sport is getting faster and faster,” she said after the race, according to the World Athletics website. “I’m just looking for what barriers can be broken down. I just speed up from here.
“I ran the race the way Bobby (Kersee, his trainer) wanted. I knew coming home that if I just kept my pace and stayed on the stride pattern we could do it and that’s came.
“The level of the 400m hurdles is clearly improving. We have a full group of girls who are ready to push their bodies to the next level and we are seeing the times drop,” added McLaughlin.
Olympic bronze medalist Bol said: “I raced against the best in the world, Sydney is just really strong.
“She was so up front at the end so I was always doubting if I really had a good race because it was very good. Then I saw the time and I was like ‘Wow’. That’s amazing to be part of it and to finish second in such a race,” added Bol.
Muhammad, who won silver in the same event at Tokyo 2020, said she had “mixed emotions” about her performance.
“It’s good to have a medal, but I came to these championships with the strength of having always medaled in all the championships, despite all the injuries. But as a competitor, you always want more.