In the final trials for this year's Commonwealth Games in Delhi in October, the 28-year-old Aberdonian led from the start and won in 3:50.73. Andy Hunter was second in 3:53.08, which was just outside the qualifying time.
Hannah Miley also hit form. She won the 200m individual medley in 2:14.41 and finished second to double Olympic champion, Rebecca Adlington, in the 200m freestyle.
Carry switched clubs and coaches after the Olympics in Beijing – he is now with Sean Kelly at Stockport Metro – and he admits it has been tough to stay motivated to keep competing at the highest level.
"I had to re-evaluate after the 2008 Olympics and I'm thrilled to have gone so quickly tonight," he said. "I've been working hard on my turns because they have always been my bugbear and this has been a massive boost.
"I'll be going for the 400m and 200m freestyle in Delhi and we will also have a great chance in the 4 x 200m freestyle relay. It has been a hard two years, but I still think I have potential to keep moving forward."
Miley will be another serious medal contender in Delhi, and she described her two swims as "very solid", more so in that she had put in some punishing training sessions last week.
Andy Mayor was the third Scot to claim a title in the opening evening. He won the 200m butterfly in 2:00.24 to make sure of his first Commonwealth Games appearance.