The 21-year-old led from the start with a dominant display to regain the title she last won in China in 2008 but could not defend last year because of injury.
Defending champion Sarah Walker was second, with Alise Post in third place.
“It’s absolutely amazing – I’m emotional at the moment but the feeling is so good,” she said afterwards.
“Missing last year was one of the hardest things, but every day that went past I was digging more and more, and it’s paid off.”
Victory for Reade, from Crewe, will help bury the memory of her disappointing failure at the Beijing Olympics.
Having gone into the event as hot favorite she crashed out in the final and missed out on a medal.
An unrelated shoulder injury saw her miss last year’s event but she was back to her best in Pietermaritzburg, leading by a bike length off the start ramp.
If you think you can’t do something, think again.