Max was a youth player at Fleetwood before he made the move to Manchester United in 2016. During his time at the club he worked alongside Kieran O’Hara, David De Gea as well as his brother Sam.
Having departed the Premier League giants in 2018 on a free transfer, he moved north east to Sunderland joining up with former manager Jack Ross. Having gained valuable experience at the club, training with Scottish International goalkeeper Jon McLaughlin, Max made a total of seven appearances in the Premier League 2 Division over the 12 months he spent there.
In July 2018, Johnstone spent a year at St Johnstone under Tommy Wright where he worked alongside current goalkeepers Zander Clark and Elliot Parrish.
Max then moved back to England signing for National League North side AFC Fylde on 10th September 2020.