Spendolini-Sirieix, whose father Fred – the chef and TV personality – was nervously watching poolside, and Toulson grabbed the medal with a superb final dive to lift them up from fourth.
As the pair completed the dive, Fred leapt from his seat in celebration and Spendolini-Sirieix, 19, and Toulson, 24, were in tears after Canada failed to better their score.
It meant Great Britain, who scored 304.38 points from their five dives, finished behind China, who have taken gold in all three diving events so far and dominated this event with 359.10, and North Korea on 315.90.
Spendolini-Sirieix and Toulson’s performance also kept up Britain’s record of winning a medal in every diving event.
Tom Daley and Noah Williams won silver in the equivalent men’s competition while Yasmin Harper and Scarlett Mew Jensen took bronze in the 3m synchronised springboard on day one.
