Johnson was born in Hendon, London.[1] He was first registered as a first-team player at Barnet as a 16-year-old in October 2010, and featured on the bench in several games in the 2010–11 and 2011–12 seasons.[citation needed] He signed his first professional contract in May 2012, and finally made his debut when he started a League Two match at home to Torquay United on 6 November 2012.[2] He scored his first goal for Barnet in a 3–2 defeat at Accrington Stanley on 16 March 2013.[3]
Johnson was part of the team that won the Conference Premier in 2014-15 and was Barnet's first choice left back for eight seasons. He left the club at the end of the 2019-20 season, after 270 appearances, scoring five goals.[4]