Three members of Britain's four-man team — Nick Skelton, Ben Maher and Peter Charles — rode clear rounds in the jumpoff to give the host team the victory. The fourth member was Scott Brash.
Skelton, 54, broke his neck in 2000 but returned to the sport two years later. Charles previously competed in two Olympics for Ireland but changed his citizenship to British in 2007.
Competing in his fifth Olympics, Skelton said he was more nervous watching his teammates than riding himself.
"I wish I could have gone four times," he said. "They've done great. I've got a wonderful horse, wonderful owners, it's a dream come true."
The last time Britain won an Olympic gold medal in show jumping was at Helsinki in 1952.
Scores from the final round in the team competition were combined with scores from the first round Sunday.
Saudi Arabia held the lead with only one penalty point after the first round and four countries, including Britain and the Netherlands, were tied for second with four faults each.
The height of obstacles and the striding between fence combinations were made more difficult for Monday's final round, resulting in more dropped fence rails and a wide swing in the results.
The British and Dutch had 8 faults each to put them into the jumpoff Monday. Saudi Arabia took bronze with 14.
Canada was fifth. Ian Millar of Perth, Ont., Eric Lamaze of Schomberg, Ont., and Jill Henselwood of Oxford Mills, Ont., had 26 faults.
The team competition also served as a qualifier for the individual show jumping event when the top 35 riders out of 75 entries advanced. The final individual round will be held Wednesday, when medals will be presented.
Skelton and Maikel van der Vleuten and Marc Houtzager, both of the Netherlands, are tied for first with no faults going into Wednesday's round. Edwina Tops-Alexander of Australia, Prince Abdullah Al Saud of Saudi Arabia and Ben Maher of Britain are tied for second with four faults each.
American Rich Fellers and Millar, who is competing in his 10th Olympics, are among a group of riders tied for 11th with 8 faults each.