He was drafted to Essendon as a rookie after playing underage with the Calder Cannons in the TAC Cup competition.

On 15 October 2007, Essendon announced that 29-year-old Johnson was to be delisted by the club, giving him the option of nominating for the national draft.

[2] The decision to delist Johnson was unpopular to many Essendon fans who enjoyed Mark's 'hard at it' attitude to his footy.

[3] In the 2007 AFL Draft however, he was drafted to West Australian club, Fremantle, where he was reunited with former Essendon teammates Dean Solomon, who was traded by Essendon in 2006, Kepler Bradley, also delisted by the club at the end of the 2007 season, and former player and assistant coach Mark Harvey, who had just been appointed Fremantle coach.

[4] He later sustained a career ending shoulder injury and played his last game in round 22 against Collingwood, which Fremantle won by 24 points.