Watson attended St George's College, Weybridge in Surrey, as a full-back.

Watson started his career at London Irish in 2009,[1] where he came through the club's academy.

Watson never made a competitive first team appearance for Saracens but did help them win the JP Morgan Premiership Sevens.

Watson transitioned back to 15-a-side[2] when he signed with Newcastle Falcons after three years with England Sevens in February 2015.

Marcus played for England national rugby sevens team from 2012–2015.