Mason is an attacking midfielder who can also play as a forward. He made his debut for the Manchester United Under-18 side whilst still an Under-16 schoolboy in August 2017 and scored a hat-trick in October 2017.
Following an excellent 2017/18 season, Mason went on pre-season tour with the First Team in the summer of 2018. He scored his first hat-trick of the 2018/19 season in September 2018 against Blackburn Rovers. He scored on his Under-23 debut against Wolverhampton Wanderers in October 2018. He scored a hat-trick in the third round of the FA Youth Cup against Chelsea in December 2018. He made his First Team debut in March 2019 away to Paris Saint-Germain.