Stevenage, Boreham Wood, St. Albans City
Johnson started his career in the youth system of West Bromwich Albion, where he spent seven years as a schoolboy. In the summer of 2013, Johnson was offered a scholarship by the club but opted to leave and join Stevenage, where he felt he had a better chance of playing first team football. Johnson started training with the first team straight away, alongside starting a two-year scholarship. Johnson appeared numerous times on the bench throughout the 2013–14 season, making his professional debut in May 2014 in the 2–0 defeat to Brentford. He became Stevenage's youngest ever debutant at the age of 17 years and 215 days.