The 26-year-old paced himself to perfection in the final laser run having led throughout the competition and becomes the first British man to win an individual Olympic medal in a sport that has been in the programme at every Games since 1912.
Choong looked like he might be overtaken by Egypt’s Ahmed ElGendy heading into the final 800 metres lap but the British athlete had something in reserve and he sprinted across the finish line.
French was the sixth British woman to win a medal in the sport since 2000, but the men had always fallen just short until now.
Choong, from Kent, rates fencing and swimming as his two strongest disciplines, and he certainly lived up to that, topping the table from Thursday’s fencing with 25 victories and 10 defeats.
He then finished third in the 200 metres freestyle swim just behind team-mate Jamie Cooke, who was back in 16th after the fencing, before adding another two points in the fencing bonus round.
That left him 19 points ahead of Jung Jin-hwa of South Korea heading into the show jumping, which caused such a stir on Friday when German leader Annika Schleu tearfully tried to get her horse to cooperate and scored zero points.
Schleu’s behaviour towards Saint Boy was the subject of much conjecture on social media and her coach, Kim Raisner, was thrown out of the Games for punching the animal.
There was less drama in the men’s event, with the leaders mostly keeping their hopes alive.
Cooke had a good round, knocking only one fence down, with Jung matching that. Choong, riding the same horse on which French managed a clear round, clattered through the first fence but only had one more down to keep his nose in front.
Choong was second in Rio going into the laser run only to struggle on the range and finish 10th, prompting him to quip about his Tinder profile and his trigger control.
Choong had good reason to feel confident having won the World Cup Final, which doubled as the test event, in Tokyo in 2019, as well as a World Cup in Bulgaria earlier this year.
His 12-second lead going into the laser run was relatively slim but he shot well, missing only five shots in his four visits to the range.
ElGendy surged up from 13th but had expended more energy than Choong in getting there and the British athlete judged his effort to perfection.
Cooke maintained his positioning after the show jumping to finish ninth.
Choong was relieved to have held off the challenge of ElGendy in the closing stages of the laser run.
“I was thinking down the last straight ‘he’s going to catch me’,” he told the BBC.
“I’ve always said I wanted to be the best in the world at something and this is a dream come true.
“My swimming was good, my fencing was good. My shooting was a bit sketchy again. But I pulled myself together and this time I’ve nailed it.”
On becoming the first British man to win an individual modern pentathlon medal, Choong joked: “To be honest I couldn’t let Kate have all the limelight.”