Four years after reluctantly watching the Beijing 2008 Games on television following a career-threatening foot injury, Ennis made light of the weight of expectation on her shoulders to leave her rivals battling for silver and bronze.
Three personal bests in the previous six events meant Ennis went into the final event, the 800m, with a commanding 188-point lead that equated to a 13-second advantage over Lithuania's Austra Skujyte.
A run of 2:05.69 would have seen her become only the fourth woman in history to score 7,000 points, and even though there was no need for such heroics, the 26-year-old blasted through the opening lap on her way to victory in 2:08.65.
Lilli Schwarzkopf of Germany took silver, with Tatyana Chernova of Russia taking bronze.
'I can't believe I've had the opportunity to come to my first Games in London and won an Olympic gold medal. It's unbelievable,' said Ennis.
I can't believe I've had the opportunity to come to my first Games in London and won an Olympic gold medal. It's unbelievable.Jessica Ennis
'It's a massive relief because it's so hard getting through a Heptathlon anyway, it's just such a tough event.
'But to have come into this event with all that pressure, and everyone just saying, "Oh, you're going to win gold, you're going to win gold" - and I know how hard it has been to win it - yeah, I just can't believe I've done it.'