In the last showjumping stage at Chateau de Versailles on Monday, world number one Ros Canter and Tokyo 2020 champions Collett and Tom McEwen secured the win.
With 91.30 penalties, Team GB finished the three-day team tournament 12.3 points ahead of the host nation, France. Japan secured the bronze medal.
In the jumping final, Collett made a comeback and won her second medal of the day without using any penalties. McEwen placed fourth, while Australian Christopher Burton and German gold champion Michael Jung finished first and second, respectively.
GB’s first team eventing victory in 49 years came from Collett, who was riding London again.
For the first time since winning back-to-back gold medals in 1972, the team successfully defended their Olympic title three years after that triumph.
Collett, who almost died in a fall in 2013, put on a flawless performance to become the first British woman to win an individual eventing medal since Kristina Cook in 2008. The British celebrations did not finish there.
“I never imagined that today would arrive,” Collett said to Sport.
“I owe that horse everything at all.” It’s feasible because of the team. To each and every one of them, I simply want to say thank you.