Duffy who won the championship in 2021, 2017 and 2017, finished her race in the Abu Dhabi heat with a time of 01:53:24.
The Olympic and Commonwealth champion finished over a minute faster than Great Britain's Georgia Taylor-Brown (28) to secure gold. Germany's Lena Meissner (24) won bronze.
"I'm really, really proud of this one," Duffy said. "It was a difficult start to the year for me coming out of the Olympics and Covid and it took a lot of work to get my mind back into it so I'm thrilled."