The 19-year-old, who has a form of muscular dystrophy, was already the Paralympic, World and European champion in the event.
And he was in a class of his own in Glasgow, finishing in two minutes 22.76 seconds – 0.10 seconds outside his European record.
“I was so close to my best time and am really happy with that,” he said.
“I dropped a lot of time from this morning’s swim and that was one thing I really wanted to do this evening. I have a good endurance base and that transfers well into the medley.”
Silver went to Australia’s Jesse Aungles ahead of his team-mate Blake Cochrane.
Hynd will now aim to retain his European title at the IPC Swimming European Championships, which begin in Eindhoven on Monday, 4 August.
The medley is Ollie Hynd’s event and a world record could have been on today but maybe he just didn’t have the people around to push him enough.