At competitions in Fort Lauderdale, Florida, Walsh crossed the finish line in a time of 54.33 seconds, 0.27 seconds faster than his previous record.
The new record time now means that the American is more than a second faster than Sarah Sjöström, who was the second-fastest of all time with 55.48 seconds.
Sjöström recently made a comeback after becoming a mother, with the goal of participating in the European Championships this summer and, in the longer term, the Olympics in Los Angeles in two years.
