After two years of injuries and numerous obstacles, the 30-year-old had stared down the world record holder and won her second world 100m hurdles title.
"I don't know if it was surprise or what, but the emotion just escaped my body because I was so excited and so happy to have achieved what I have worked so hard for", Pearson said.
American veteran Dawn Harper Nelson was second, .04 seconds behind, and Pamela Dutiewicz of Germany took bronze in 12.72.
Harrison - who was the 1/6 on favourite for the title and had not been beaten in a race since the US Olympic trials previous year - at least made it unlike Jamaica's defending champion Danielle Williams who flopped to finish fifth in her semi.
She joined 400m runner Cathy Freeman and 400m hurdler Jana Pittman as the only Australians to have won two world track and field titles. "On the finish line I thought I had finished fourth - madness!" "It wasn't surprise, it wasn't shock, I was just proud, so proud of what I had done to get here".
"I've left no stone unturned to get here".
"Silver tastes like gold tonight".
"I love this stadium, I love the people and I'm so happy to be back here doing the same thing again".
She then missed the Rio Olympics because of achilles and hamstring problems.
Making the victory even more special was that Pearson had coached herself for the past year.
"It took me hours and hours and hours on the first day to write a program out and decide what was best for me and what I could and couldn't do, being an older athlete, having these injury troubles".
"When I knew I felt that I knew it was in me to do it".
Pearson looked tense and focused before the race, not acknowledging the crowd when her name was called, but was hugely impressive quickly overhauling early leader Jamaican champion Megan Simmonds and opening a sizeable lead. But when she clocked 12.48 seconds in the London Diamond League last month - her fastest time for five years - she realized she was in medal-contending form.
The Australian still holds the world championships record of 12.28sec from her victory in Daegu in 2011.