The 20-year-old from Midlothian ran 1:50.36 to add the British Universities and Colleges outdoor title to the indoor crown he won earlier this year, producing a late burst in a tactical race.
However, the Scottish junior record holder revealed he had to overcome the after-effects of food poisoning and jet leg to pull off the result.
"I've been training over in California for the last month so I was feeling pretty tired after flying back for this," he said. "And just before I left, I took ill from something I ate in San Francisco which didn't help. But I had two good races over there and set a new personal best. I came here with the aiming of winning, either by going hard from the front or sitting back and going tactically. It turned out to be the latter option but it gives me a lot of confidence for what's coming up."
Fellow Scot Ray Bobrownicki won the high jump title with a leap of 2.15 metres while Eilish McColgan was forced to settle for silver in the 1500m.
""I'm a bit disappointed with second," she said. "I got boxed in badly." Lynsey Sharp was fifth in the 400m.