Marquand spent his childhood near Cheltenham and, although not from a racing background, grew up around horses. After pony racing and riding out for local trainers, he joined the Wiltshire yard of trainer Richard Hannon as an apprentice at the age of 16. 

Marquand rode his first winner in 2014 and was champion apprentice jockey in 2015. That year he reached the finals of the BBC Young Sports Personality of the Year. 

In 2018 he rode more than 100 winners, including Anna Nerium in another Group 3 race, the Supreme Stakes at Goodwood. Over Christmas and the New Year he spent six weeks in Australia riding for the Sydney trainer John O’Shea. Another trip to Australia in March–April 2020 provided Marquand with a Group 1 double on the William Haggas-trained Addeybb in the Ranvet Stakes and the Queen Elizabeth Stakes. Marquand also had several successes in Group 3 races in Australia and was nicknamed ‘Aussie Tom’ by Australian racing fans. 

On 4 July 2020, Marquand had his first ride in the Epsom Derby. He had ridden English King to win the Lingfield Derby Trial but lost the Derby ride on the fancied runner to Frankie Dettori. Instead, he secured a ride on 50/1 outsider Khalifa Sat and finished in second place behind Serpentine. 

Marquand’s first Classic win came on Galileo Chrome in the St Leger Stakes at Doncaster on 12 September 2020. He had only been given the ride the previous day, whenjockey Shane Crosse tested positive for Covid-19. 

Marquand had a career-best 176 winners in Great Britain in 2021, including a Group 1 victory in the July Cup on Starman, trained by Ed Walker. Addeybb provided him with a further Group 1 in Australia when he won the Queen Elizabeth Stakes for the second year in a row. 

Marquand has become one of the very finest operators on the flat in both Southern and Northern Hemispheres and looks to add the coveted Flat Jockeys Championship to his illustrious roll of honor in 2026 and beyond.