British-born Tunnicliffe came back from ninth to take gold
American Anna Tunnicliffe won sailing gold with 37 points after the 10 races of the women's Laser Radial class.
British-born Tunnicliffe, originally from Doncaster, was ninth midway through the race, but came back to take second in the race and first overall.
Lithuania's Gintare Volungeviciute took silver, while bronze went to China's Xu Lijia.
Britain's Penny Clark finished in 10th place overall in the standings, after coming seventh in Qingdao.
Tunnicliffe moved to the US when she was aged 12.
The 25-year-old was struggling in the medal race until she benefited from a large wind shift that propelled her from ninth to third.
"It was a little too exciting," she said. "I had a really bad start. It was very hard to focus when my competitors were gaining points on me."
"I saw this big left puff, and I went like 'here goes'. I had to. I mean I was guaranteed a medal, and that meant a lot, so it was a risk worth taking," she said.
"I went left and moved to the front of the fleet."
She went on to sail in second behind Volungeviciute and finish in the top spot overall by five points.
Xu - one of two strong Chinese sailing medal hopes, along with windsurfer Yin Jian - benefited from the vocal home support on the main breakwater at the Olympic Sailing Centre to finish third, both on the day and overall.
China have never won Olympic sailing gold, although Yin has an opportunity to end that run on Wednesday when she takes a five-point lead into the medal race.