The crew of Alex Gregory, Pete Reed, Tom James and Andrew Triggs Hodge secured Britain's fourth straight Olympic victory in the event in dominant fashion, leading from start to finish to cross in 6 minutes, 3.97 seconds. Australia was a half-length behind in second and the United States took the bronze.
Britain, the reigning world champion, maintained its dominance of the discipline that stretches back more than two decades to the days of rowing greats Steve Redgrave and Matthew Pinsent.
The gold was Britain's seventh medal of the regatta — and third gold — to surpass its total from Beijing four years ago, making it the country's biggest rowing haul in the modern era.
Their victory also denied Australia's Drew Ginn a fourth gold in four Olympic Games — a feat that would have been a first for an Australian.
Triggs Hodge, the British stroke, repeatedly punched the air after sealing victory and the four crew members got in a huddle on the jetty after climbing out of the boat.
The Australians and the British then embraced, a friendly ending to months of mind games and trash talk by the rival crews.
Ginn said Australia would turn the final into a "drag race," going out hard from the start, but it was Britain which took the early lead by 0.3 seconds after 500 metres.
The cushion was 0.6 seconds at the 1,000 and 1,500-meter markers and Britain held on comfortably as they were roared home by the crowd, winning by 1.22 seconds.
The bronze for the U.S. crew of Glenn Ochal, Henrik Rummel, Charles Cole and Scott Gault was the country's first medal in the event since the Barcelona Games in 1992.