Stimpson, a silver medal winner in the World Triathlon Series in 2013, sprinted clear with 400 metres remaining of the final 10km run to win a thrilling race that started with a 1.5km swim in and a 40km cycle around Strathclyde Loch.
Canada's Kirsten Sweetland claimed silver, with England's Vicky Holland taking bronze in warm, sunny conditions, with water temperatures of 20.9 degrees Celsius and air of 21.8.
With a lap to go of the gruelling run, Stimpson was joined by Sweetland and fancied Australian Emma Jackson, who had done well to make up a 25-second deficit from the swimming, in a lead group of five.
As Stimpson ramped up for the final push, Hewitt and Holland struggled, and then Sweetland was left gasping for air as the 25-year-old English triathlete accelerated away for the line in brilliant sunshine.
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Triathlon is returning to the Commonwealth Games programme for the first time since Melbourne 2006, having made its debut at Manchester 2002.
The men race in their individual Olympic distance event later Thursday, with the triathletes back in action on Saturday, albeit in the sprint distance mixed team relay, an event that makes its Games debut.