Under the bright lights of Rio de Janeiro's Carioca Arena in 2016, she bowed out aged 26 as a double Olympic champion.
The girl from Middletown, Ohio, went where no other American had ever gone before in her career, dominating judo's half-heavyweight division for almost a decade.
But her journey was anything but easy. To get to the top of the podium, Harrison had to climb from rock bottom.
"If I didn't have that when I was a teenager, I might not even be here."
Salvation in sport
Sexually abused by her first coach as a teenager, Harrison often considered abandoning her ambitions -- even contemplating suicide.
She thought about running away to faraway places; of being a barista in New York, "where no-one would know me or look at me."
Sport provided the light at the end of the tunnel.
Harrison moved to Boston aged 16 in search of a fresh start after her ordeal, training under US Olympic coach and former world champion, Jimmy Pedro.
It took time to banish her demons and, at least at first, the last thing she wanted to do was train or study.
"There were days when my teammates would drag me out of bed and drive me to school, and they would watch me walk through the school doors," Harrison recalled.
"I didn't want to lift weights, I didn't want to go to school, or go to therapy, but I had no choice. If I wanted to be in the judo house, I had to follow the rules."
The budding judoka was working 50 hours per week at a hardware store in order to pay the rent, alongside her lessons in the classroom and on the tatami.
But gradually judo's self-discipline was instilled and her fighting spirit shone through.
The results soon followed, with Harrison twice crowned US senior national champion before her 18th birthday.
Top of the world
While the teenager was quickly making a name for herself as one of the most talented Americans the sport had seen, it was another thing entirely to do it on the global stage.
Harrison, though, was just getting started. A gold medal at the Junior 2008 World Championships in Bangkok proved she had what it took to beat the more established nations.
And so it proved, with Harrison topping the podium at the senior World Championships two years later in the home of judo, Japan.
A host of Grand Prix and Grand Slam titles followed in her half-heavyweight division, leading up to the 2012 London Olympics, where Harrison was among the favorites.
Just months before the Games, a partial tear to her medial collateral ligament left her knee the size of balloon, but she wasn't about to let that stop her.
Instead, she defeated longtime rival Mayra Aguiar and home favorite Gemma Gibbons to end a 48-year wait, becoming the first American -- male or female -- to win Olympic gold.
Harrison had fulfilled her childhood ambition and was, indisputably, the world's best in her under 78kg division.
She also transcended the sport, bravely using her newfound platform to speak out about the horrors she had endured, and setting up the Fearless Foundation
in order to help others in similar positions.
Out on a high
Four years later, the Rio 2016 Olympics placed her among truly exalted company.
There Harrison bowed out from the sport on the grandest stage of all, with Aguiar and French star Audrey Tcheumeo below her on the podium and a second gold medal around her neck.
No other American judoka has come close to emulating her since, but Harrison is eager to point out that she couldn't have done it alone.
"I'm not the only one who has made sacrifices," she said. "My coaches, my family, every doctor who has taped my knee or helped me recover from an injury, anyone who's taken a fall for me or sparred with me, helped me be successful.
"It's a hard lifestyle. I spent half my life living from a suitcase, going to Japan, Germany, the UK... But I wouldn't change a second of it because it gave a kid from a middle of nowhere town in Ohio a chance to see the world.
"It speaks volumes about my coaches and my teammates that they were able to drag me from rock bottom to the pinnacle."