Canada’s McIntosh is becoming one of the stories of the Games, with the teenager tipped to break numerous records in her career.
She has already started in Paris, touching home in the 200m individual medley in an Olympic record 2:05.56 to ensure a fourth medal at her debut Games.
“For sure it was painful. Winning gets rid of all the pain,” she told the BBC.
“I was screaming at myself under water a few times because I could tell that I was behind.
“I knew that I just had to keep going and I just had to push through that wall.”
She previously took gold in the 200m butterfly and 400m medley, along with silver in the 400m freestyle.
Americans Kate Douglass and Alex Walsh won silver and bronze respectively, before Walsh was disqualified before she had even left the pool for an illegal turn from backstroke into breaststroke.
That meant Australia’s Kaylee McKeown was upgraded to bronze.
McKeown later joined her team-mates for the mixed relay, with the Australians securing bronze.
The United States won gold in 3:37.43 and China silver, but Britain’s quartet of Kathleen Dawson, James Wilby, Duncan Scott and Anna Hopkin struggled from the off and finished well out of the medals.
France, with Leon Marchand swimming the second leg, finished fourth – the first time the host nation’s poster boy has appeared in a final in Paris and not won a medal.