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The 23-year-old beat her Games record, clocking eight minutes 18.11 seconds.
England's Sophie Taylor, 18, won gold in the 100m breaststroke final, with team-mate Ollie Hynd, 19, taking the Para-sport 200m individual medley SM8.
Aimee Willmott, 21, and Adam Peaty, 19, added silvers for England in the 200m butterfly and 50m breaststroke.
And England's Adam Barrett, 21, ended the session with bronze in the 100m butterfly.
Welsh celebrations were perhaps more pronounced given Carlin, from Swansea, was the first woman from her nation to win a Games swimming title since Pat Bevan in the 200m breaststroke in Christchurch in 1974.
It was Wales' fourth swimming medal of Glasgow 2014 and Carlin now has a complete set of Commonwealth Games medals, having won silver and bronze in Delhi in 2010.
"I'm just so happy to come away with the gold," she said of a race in which Scotland's Hannah Miley, 24, and Camilla Hattersley, 19, were fifth and seventh respectively.
New Zealand's Lauren Boyle, 26, took silver and Canada's Brittany MacLean, 20, bronze.
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"I can't believe it, I really can't," added Carlin. "I put everything into my training this year. The support has been overwhelming and obviously I'm just so glad."
Harrogate's Taylor, meanwhile, had trailed at the turn in the 100m breaststroke but roared back to beat Australia's Lorna Tonks, 25, and Alia Atkinson, 25, of Jamaica in a time of 1:06.35. Scotland's Katie Armitage, 18, was eighth.
Uttoxeter's Peaty - who won the 100m breaststroke on Saturday, could not quite produce a similar comeback in the 50m breaststroke, finishing two hundredths of a second behind world-record holder Cameron van der Burgh.
The 26-year-old South African's time of 26.76secs enhanced the Games record he set in the semi-finals.
Scotland's Mark Tully, 22, was denied bronze by just one hundredth of a second, third place going to Cristian Sprenger, 28, of Australia.
Tully's team-mates Ross Murdoch, 20, and Joe Welstead, 24, were sixth and seventh respectively.
Middlesbrough's Willmott - who was runner-up in Thursday's 400m individual medley behind Miley - claimed her second silver in the 200m butterfly.
Canadian Audrey Lacroix, 30, earned gold and Australia's Maddie Groves, 19, took bronze, with the Welsh duo of Alys Thomas, 23, and Jemma Lowe, 24, fourth and fifth respectively. Scotland's Miley finished sixth.
England's fifth swimming medal of the night came with bronze from Barrett in the 100m butterfly.
The Reading athlete qualified fastest for the final but could not thwart South Africa's Olympic champion Chad le Clos, 22.
Clos added to his gold in the 200m, silvers in the 50m and 4x100m free and bronze in 4x200m free, in a Games-record time of 51.29secs.
Joseph Schooling, 19, won bronze for Singapore and England's James Guy, 18, was sixth.
In the other two events Australians filled the podium, with England's 50m freestyle and 50m butterfly champion Fran Halsall denied a third medal at Tollcross when she finished fourth in the 100m freestyle.
Australia's Cate Campbell, 22, posted a Games record of 52.68secs to win ahead of sister Bronte, 20. Team-mate Emma McKeon, 20, won bronze.
And in the 200m backstroke, Australia's Mitch Larkin, the 21-year-old who took silver in both the 50m and 100m, earned gold ahead of Josh Beaver, 21, and Matson Lawson, 22.
Scotland's Craig McNally, 21, was some way short of his personal best in fifth, one place ahead of team-mate Ryan Bennett, the 23-year-old who represented England in Delhi four years ago.
Welshman Xavier Mohammed, 24, was eighth.
Jazz Carlin became the first Welsh woman to win Commonwealth Games gold in the pool in 40 years when she eased to victory in the 800m freestyle.