Marchant’s former athletics coach Toni Minichiello, best known for his work with Olympic champion heptathlete Jessica Ennis-Hill, was the first person to spot her cycling potential when he noted the impressive power figures she had produced during Wattbike tests.
Although she has represented Great Britain in track and field at the 2012 World Junior Championships, and despite being nothing more than a leisure cyclist on road and mountain bikes, Marchant impressed during a six-week trial period with the Great Britain Cycling Team, joining the Senior Academy in April 2013 and earning promotion to the Podium Programme in October of that year at the age of 20.
By then, Yorkshire-born Marchant had already demonstrated her promise with silvers in the team sprint, with Victoria Williamson, and keirin and a bronze in the sprint at the British National Track Championships in September.
With her future career clearly lying in the explosive sprint events - both team and individual - Marchant progressed to the international stage at the 2014 UEC Under-23 European Track Championships in Anadia, Portugal where she won bronze medals in both the keirin and team sprint, alongside Rosie Blount.
Her development was again highlighted at that year’s National Track Championships with podium finishes - although no golds - in the sprint, keirin, 500-metre time trial and team sprint, where she continued her partnership with Williamson.
A first gold medal breakthrough seemed imminent and it duly arrived at the 2015 UEC Under-23 European Track Championships in Athens where she won the keirin and took a silver with Williamson in the team sprint.
By then, she had also made her debut at her first UCI World Track Cycling Championships in Paris, where she represented Great Britain in the 500-metre time trial, posting a personal best before finishing in 13th place.
An indication of her progress could be seen at the 2015 National Track Championships, however, where Marchant ended her wait for a victory by winning an astonishing four gold medals - in the sprint, keirin, 500-metre time trial and team sprint, in a new pairing with Jessica Varnish.
That form continued into 2016, where Marchant medalled for the first time in a UCI Track Cycling World Cup meeting, winning silver in Hong Kong with Varnish in the team sprint as Great Britain sought to win qualification for a place in the event at the 2016 Rio Olympic Games.
Unfortunately, at the UCI Track Cycling World Championships in London in March 2016, the team of Marchant and Varnish could only qualify in fifth place, missing out on a medal ride and a place at the Olympics by less than one second; a disappointment which left Katy seeking selection for Rio in an individual discipline.
That led to a superb campaign in the sprint at the Olympics in which she qualified second fastest in the flying lap behind team mate Becky James. In the match sprint portion of the competition, Marchant advanced through three rounds without losing a race until meeting eventual Olympic champion Kristina Vogel who beat her in the semi-finals. The consolation for Marchant was a dominant win in the bronze-medal ride against Dutch rider Elis Ligtlee.
Marchant paired up with Senior Academy rider Sophie Capewell for the 2017/18 Tissot UCI Track Cycling World Cup season - the duo improving with each round and just missing out on a bronze medal at round three in Milton, Canada, finishing in fourth, the pair's best result as a team.
The former-heptathlete overcame that disappointment by qualifying for the keirin final - winning silver to claim her first-ever individual world cup medal.
In 2018, Marchant was selected to represent Team England at the Commonwealth Games in Australia and teamed up with Lauren Bate for the team sprint with the duo overcoming the Welsh pair of Rachel James and Ellie Coster to win bronze.
Late in 2019, she enjoyed her first taste of world cup success, producing a scintilating combination of rides to win the keirin in front of a home crowd in Glasgow.
|Commonwealth Games, Gold Coast (Australia)||Team sprint||Bronze|
|UCI Track Cycling World Cup, Milton (Canada)||Keirin||Silver|
|Olympic Games, Rio de Janiero (Brazil)||Sprint||Bronze|
|UCI Track Cycling World Cup, Tseung Kwan O (Hong Kong)||Team sprint||Silver|
|UEC European Junior and Under-23 Track Cycling Championships, Athens (Greece)||Keirin||Gold|
|UEC European Junior and Under-23 Track Cycling Championships, Athens (Greece)||Team sprint||Silver|
|UEC European Junior and Under-23 Track Cycling Championships, Anadia (Portugal)||Keirin||Bronze|
|UEC European Junior and Under-23 Track Cycling Championships, Anadia (Portugal)||Team sprint||Bronze|