The 23-year-0ld had been a junior heptathlete training alongside Jessica Ennis-Hill in Sheffield three years ago, when coach Toni Minichiello noticed the power output she produced on a watt bike and suggested she try track cycling.
A difficult journey ensued, which included moving to Manchester and slowly picking up the sport.
And when she was part of the women’s sprint team that failed to qualify for Rio at the world championships back in the Spring, she must have felt her Olympic dream was over.
But after sealing an individual spot she fought through three rounds of qualifying over two days to reach the medal round. Then Marchant picked herself up from defeat to eventual winner Kristina Vogel in the semi-final to beat the Netherlands’ Elis Ligtlee 2-0 in the best-of-three race.
Marchant watched London 2012 having finished 21st in the heptathlon at the World Junior Athletics Championships one month before.
The 23-year-old eased through Sunday and Monday’s earlier rounds and also Tuesday’s quarter-finals before then coming unstuck against double sprint world champion and eventual gold medallist Kristina Vogel 2-0 in the best-of-three race semi-final.
“I cannot believe it, I am so happy that all the hard work, tears, sweat paid off and I couldn’t be happier,” she said.
“I think I owe Toni Minichiello a massive thank you. To finish with a bronze medal I cannot believe it.
“I could not have imagined that medal this time last year. It was a massive thing for me to get selected, I really had to prove myself to get the coaches and selectors on side.
“They had so much belief in me, walking away with a bronze medal I just can’t believe it.
“This is just the beginning for me. Obviously I’m ecstatic to come away with a bronze medal, this was never what I imagined.
“I’m really excited to get back to Manchester now and have a little bit of a break and then get working again and see what the next four years has got ahead for me.”
Team-mate Becky James won silver after defeat to Vogel.
Peerless Trott became a four-time Olympic champion after winning her second gold of the 2016 Games in Rio.
The 24-year-old from Cheshunt took a commanding 24-point advantage into the points race, which concluded the six-discipline omnium, and rode a masterful race.
Trott, who won team pursuit gold on Saturday, successfully defended the title she won at London 2012 to take her to four career Olympic gold medals, the most for a female British Olympian.
The Briton finished with 230 points, 24 clear of her nearest rival, after enhancing her advantage in the discipline which was once her Achilles heel.
Sarah Hammer of the United States was second on 206 points and Belgium’s Jolien d’Hoore third on 199.
Trott said: “I can’t believe it – I did not expect that at all.
“I am just so happy that it all came together – I can’t thank everyone at home enough.”
Trott added: “To be able to repeat my success in London – I can’t explain what I am going through right now, I am so, so happy.”