Alistair Brownlee pulled away over the closing minutes of the 10-kilometer run that concludes the race and became the first athlete from Britain to medal in the event since it became part of the Olympics in 2000.
Javier Gomez of Spain took the silver medal, finishing 11 seconds behind the older of the two Brownlees.
Jonathan Brownlee suffered a 15-second penalty for climbing onto his bike too early in the transition between swimming and cycling but still was able to finish third.
The Olympic triathlon consists of 1.5 kilometers of swimming and a 43-kilometer bike ride before the 10 kilometers of running -- all taking place within the confines of Hyde Park.
Simon Whitfield, Olympic gold medalist in 2000 and the silver medalist in 2008, suffered an accident on his bike and abandoned the race. He had been 31 seconds behind at the end of the swimming portion of the event.
Alistair Brownlee was 12th in the 2008 Olympic triathlon, but since then has twice finished a year as the world's top-ranked triathlete.