Marchant joined the Harlequins academy in 2014 and made his club debut against the Newcastle Falcons in May 2015. On 10 November 2019, the Blues, Auckland's Super Rugby team, announced that they had signed Marchant on their Instagram account. It was confirmed via their own website that he would be playing with them as part of a sabbatical clause provided by Harlequins to further his international experience and possibility of an England call up. He featured in seven games and scored three tries.
