Early career Johnson made his MMA debut in 2002, going 4–4 by years end. Johnson then made his
MFC debut losing to Chad Hanseh. Starting in October 2005, Johnson went 11–1–1 over five years with his only loss coming in a title fight for the KOTC Canadian Lightweight Championship against future
UFC top contender and training partner
Rory MacDonald. He also captured the XMMA Lightweight title. Johnson would make his return to MFC at
MFC 23 taking on Ryan Machan. He lost via submission in the first round. Johnson was set to take on Orestes Betran at
MFC 27. Betran then pulled out of the match and was replaced with a veteran of 29 fights at the time,
Ryan Healy. He won via unanimous decision.
The Ultimate Fighter In late 2013 it was announced that Johnson will be one of the Canadian fighters picked to be on
TUF Nations Team Canada. In episode 1, Johnson is picked to fight first against Australia's own
Brendan O’Reilly. Johnson states that he is injured, but that he always fights injured. Despite the injuries, Johnson implies he is still more dangerous than anybody else in the house. Johnson gives Canada their first win with a rear-naked choked in the first round. In episode 10, Johnson was set to face his teammate
Chad Laprise in the semi-finals. Johnson lost via KO in the second round. Johnson's jaw was broken from the punch. After the show Johnson was noted as the reason for the removal of fellow TUF Nations contestant Tyler Manawaroa from the UFC after claiming Tyler was a racist due to an image posted on his personal Instagram. Tyler was of native New Zealand Maori descent and later explained it was the actions of a schoolboy making fun of himself and his own heritage, as in Australia many Aboriginals, Maoris and Polynesians consider themselves 'dark-skinned' or 'non-white'. Kajan later apologised though nevertheless Tyler was removed from the UFC roster and remains inactive yet undefeated .
Ultimate Fighting Championship Johnson made his promotional debut at
UFC 174, taking on
Tae Hyun Bang. He lost via knockout in the third round. They both earned
Fight of the Night honors. Johnson was then set to face
Zhang Lipeng on May 16, 2015, at
UFC Fight Night 66. He won via unanimous decision. Johnson faced
Naoyuki Kotani on September 27, 2015, at
UFC Fight Night 75. He won the fight by unanimous decision. Returning from a near two-year hiatus, Johnson faced
Adriano Martins at
UFC 215 on September 9, 2017. He won the fight via knockout in the third round. Johnson was scheduled to face
Rustam Khabilov on March 17, 2018, at
UFC Fight Night 127. However, Khabilov pulled out of the fight citing injury and was replaced by
Stevie Ray. He won the fight via split decision. Johnson faced
Islam Makhachev on July 28, 2018, at
UFC on Fox 30. He lost the fight via armbar submission in the first round. The fight with
Rustam Khabilov was rescheduled and eventually took place on September 15, 2018, at
UFC Fight Night 136. Johnson lost the back-and-forth fight by split decision. 12 out of 13 media scores gave it to Johnson. On September 29, 2018, Johnson revealed that the fight with Khabilov was the last of his contract and the UFC had not made any attempts to re-sign him. He announced his retirement from mixed martial arts in 2020 after his release from the UFC. ==Championships and achievements==