The British pre-race favourite lived up to his status as the world's leading triathlete to give the home country another gold and its first Olympic medal in the sport.
Brownlee eventually crossed 11 seconds clear of Spaniard Javier Gomez in second, but it would have been by much more if the Englishman hadn't taken time out to savour his big moment in front of a roaring home crowd at Hyde Park.
His younger brother, Jonathan, came home third for bronze and Britain's second triathlon medal in the space of about 30 seconds.
"I took my time, but I was really tired," Alistair said. "There were hundreds of emotions. Happy, excited, overwhelmed, but a bit of relief in there as well."
Victoria's Simon Whitfield, a two-time Olympic medallist and Canada's flag-bearer in London, didn't finish after crashing early in the bike leg.
Kyle Jones of Oakville, Ont., was 25th Victoria's Brent McMahon was 27th.
Alistair Brownlee is the reigning world and European champion, and delivered under enormous pressure.
His victory also took Britain to 19 golds overall at the London Games, equalling the country's tally from Beijing with five days of competition still to come.
"We had a strategy to distance ourselves a little bit from the Olympics and the pressure," Alistair said, "but we failed with that. We've been watching loads of events."
At the end, the English brothers from the northern county of Yorkshire were together on the podium as expected as "God Save the Queen" rang out from the middle of London's famed park.
The climax was nothing like the women's race, where the gold was decided by a photo finish.
The eventual ease with which Alistair won from fellow two-time world champion Gomez also was nothing like the late exertion Jonathan was forced in to as he grimly hung on for a medal after serving a 15-second time penalty late in the run.
The younger Brownlee collapsed 10 minutes after the finish, overheating, and had to be given ice packs and glucose by medical staff, delaying the medal ceremony.
"That's part of triathlon," Jonathan said, shrugging off the treatment which held back his celebrations. "I haven't looked at my phone yet but I'm sure I'll have some messages and tweets and hopefully some new followers."
His brother added: "When you come across the finish line in a triathlon, you're normally in a bad way. It's a bit of a tough sport."
As for followers, the Brownlees had a bunch of them for much of the gruelling 54.5 kilometre swimming, cycling and running race through Hyde Park.
They were almost always among the leading pack. They stepped up the pace in the 43-kilometre cycling leg — which they finished together — and broke away from everyone except Gomez in the 10-kilometre run.
Alistair eventually found something extra to pull away from his Spanish rival about halfway through the run to clock one hour 46 minutes 25 seconds, adding the Olympic title to his world and European triathlon crowns.
He slowed right down to wave to the crowd in the stands at the end, then raised the British flag over his head before breaking the tape at a walk and dropping to the floor with exhaustion.
Seconds later he reached over to Gomez, who lay on his back on the blue matting after finishing, and shook hands with his rival.
Gomez also won his first Olympic medal, with the top three men all on an Olympic podium for the first time in their careers. Triathlon made its Olympic debut in Sydney in 2000.
"Alistair was pushing the pace really fast," Gomez said. "I knew I had to try and hang on and that's what I did. My strategy was to try to keep up as much as I can. The last three kilometres, the pace was too high for me.
"I was happy with my silver .. . I couldn't do much more today."
French pair David Hauss and Laurent Vidal were fourth and fifth, respectively, while defending Olympic champion Jan Frodeno of Germany was sixth.
Richard Varga of Slovakia had set the early pace, emerging from the swim through The Serpentine lake first. But the Brownlee brothers followed close behind, with Jonathan fourth and Alistair sixth. The hometown favourites set the tempo for almost the entire race after that, with the help of teammate Stuart Hayes, who paced them during the bike ride.
Frenchman Vincent Luis edged ahead as the competitors went from bike to run, but it was only by a matter of seconds from the Brownlees, who arrived at the final transition side by side.
Like how they stood on the podium.
At the finish line, Alistair lifted himself to his feet to greet his brother with a hug. The pair said they didn't remember what they said to each other.
"Probably well done, or something like that," Alistair said. "We were both absolutely knackered."