The final decision on Wednesday marks the first time the IOC has granted two Summer Olympics at once.
It came after a year’s worth of dealmaking by IOC president Thomas Bach, who had only the two bidders left for the original prize, 2024, and could not bear to see either lose.
Both cities will host their third Olympics.
The Paris Games will come on the 100th anniversary of its last games - a milestone that would have made the French capital the sentimental favourite had only 2024 been up for grabs.
Los Angeles moved to 2028, and will halt a stretch of 32 years without a Summer Games in the United States.