Pearson, world champion in 2011 and Olympic gold medallist in London in 2012 and with Olympic and world silvers to her name, held off Dawn Harper Nelson, one of four Americans in the field, for an emotional triumph.
She missed the last two seasons due to hamstring and Achilles injuries and a badly broken wrist and feared for her career. But when she clocked 12.48 seconds in the London Diamond League last month - her fastest time for five years - she realised she was in medal-contending form.
She then underlined that by reaching the final as the fastest qualifier in 12.53 on Friday.
Pearson did not need to go that fast on Saturday but barely noticed the clock as she posted 12.59 seconds, screaming "oh my God" repeatedly after crossing the line.
"I've worked so hard, I don't know what has just happened out there. I'm so tired but I'm sure it will sink in soon," she said.
On her joyous finish-line exclamations, she said: "I don't know if it was surprise but the emotion just escaped my body because I was so excited and so happy to have achieved what I've worked so hard for.
"I love this stadium, I love the people and I'm so happy to be back here doing the same thing again."
Harper Nelson, the 2008 Olympic champion and silver medallist behind Pearson in 2012 took silver in 12.63 ahead of Germany’s Pamela Dutkiewicz, who claimed a surprise bronze in 12.72.
"I cannot believe it, it's crazy," said Dutkiewicz. "There were so many big names in the field and since I was a girl I have been admiring Sally Pearson.
"This is like in a film. I had a flow. I am glad I caught this moment of complete flow, of complete concentration. On the finish line I thought I had finished fourth - madness!"
Favourite Kendra Harrison, who set the world record in the London Stadium last year having missed out on Olympic selection, clattered too many barriers as she did in the semis and finished fourth in 12.74.
Pearson, racing in lane three outside Harrison, blasted from the blocks and showed all her experience to concentrate on her own race as Harrison faltered.
Former men's 110m hurdles world record holder Colin Jackson described the Australian's technique as "absolutely flawless" and that, combined with her famed winning mentality and now a body again able to match her mind, took her over the line.
Harrison, who was disqualified in the semis two years ago, had been unbeaten in 23 races until the semi-final in London on Friday but her wait for a championship medal goes on.
"I'm still young, this was my first world final, people forget that because I'm the world record holder," said the 24-year-old.
"They expect me to be winning all the time but I'm pleased to be in my first world final and have learned a lot."
Defending champion Danielle Williams of Jamaica failed to make the final while last year's Olympic champion Brianna Rollins, who led an American sweep of the Rio podium, is banned for a doping violation.
(Editing by Ed Osmond and Brian Homewood)
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