Scott, 21, snuck into the final in lane eight but powered through the field to take a surprise gold ahead of Lithuania’s Danas Rapsys.
Rapsys, 23, set a world-leading time earlier this season of 1:45.12 but faded in the last 50m, with Scott finishing strongest to win in a time of 1:45.34.
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Mikhail Dovgalyuk (1:46.15) completed the podium just ahead of Great Britain’s James Guy (1:46.20).
"I didn't really know what was going on with the rest of the field. I'm just really, really happy with how it went," said Scott after the race.
I had no idea where I was in the race I just kicked on with my race plan - I was just hacking away in the last 25m and hoping.
"I was pretty relaxed in the warm up, but the crowd has been amazing all week - when I took my headphones off it was amazing.
"But I just went in with no expectations."
The gold represents Scott's third medal of the 2018 European Championships, having already claimed silver in the 100m freestyle and gold in the 4×200m freestyle relay alongside Calum Jarvis, Thomas Dean and James Guy.
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