Marchant represented England U18 winning 14 caps and scoring one try. He has also represented England U20 scoring 59 points including ten tries. Marchant was a member of the side that won the 2015 Six Nations Under 20s Championship. At the 2016 World Rugby Under 20 Championship, Marchant scored in pool stage fixtures against Italy and Australia. He scored two tries in the final against Ireland. His impressive performances at junior level earned him a call-up to Eddie Jones' 45 man senior England training squad on 1 August 2016 and the following month saw him subsequently named in the Test squad for the Autumn Internationals.