Her partner Hannah Mills became the most successful female Olympic sailor in history by winning gold in the women's 470 class.
Family and friends gathered at Hayling Island Sailing Club this morning to watch her come in first.
Mills, who carried the British flag at the opening ceremony with rower Mohamed Sbihi, won silver in London and gold in Rio with Saskia Clark in the same boat.
Mills and McIntyre have dominated the regatta at Enoshima, winning two races and only twice finishing outside the top four, and they went into the medal race with a 14-point lead.
That meant they only needed to finish in the top seven to clinch gold and they were never in any danger, crossing the line comfortably in fifth.
The victory continued a hugely successful two days for Britain's sailors, with Mills and McIntyre making it three gold medals after success for Dylan Fletcher and Stuart Bithell in the 49er and Giles Scott in the Finn on Tuesday.
It is the country's second best Olympic tally after Beijing in 2008, when they won six medals, including four golds.
Mills joined forces with 27-year-old McIntyre when Clark retired following the Rio Olympics and the pair marked themselves out as the ones to beat by winning the world championships at Enoshima in 2019.
It is a debut Olympic medal for McIntyre, who follows in the footsteps of her father Mike - the gold medallist in the Star class at the Seoul Games in 1988.
There was disappointment, though, for 2012 silver medallist Luke Patience and Chris Grube in the men's 470.
They were sitting second after eight races but dropped to fifth ahead of the medal race and that was where they finished after crossing the line in seventh.