King of the Cage After going undefeated in his first three professional mixed martial arts fights, Johnson signed with
King of the Cage and challenged Tony Lopez for his
KOTC heavyweight championship on March 26, 2010, at
KOTC: Legacy. Also being the
KOTC light heavyweight champion, Lopez was undefeated his last sixteen fights, which marked Johnson's most experienced opponent at the time. Johnson recorded the upset, using his wrestling to defeat the much more experienced Lopez via unanimous decision and becoming the KOTC heavyweight champion in just only his fourth professional fight. Johnson made his first title defense against then prospect and future
UFC light heavyweight champion Daniel Cormier at
KOTC: Imminent Danger on August 13, 2010. He lost the fight and KOTC heavyweight championship in the first round via rear-naked choke submission, resulting in his first professional loss. Johnson rebounded from his loss to Cormier by defeating Boban Simic via unanimous decision on November 13, 2010 at
KOTC: Infusion.
Bellator In April 2011, it was announced that Johnson had signed with
Bellator, with his promotional debut expected to take place at
Bellator 41 on April 16 against Carlos Flores. Johnson, however, was later replaced by Rudy Aguilar for unknown reasons. Johnson eventually made his promotional debut against current
UFC competitor
Derrick Lewis at
Bellator 46 on June 25, 2011. He won the fight via unanimous decision by 29–28 on the scorecards.
ONE Fighting Championship After being sidelined for nearly two years due to issues with his Bellator contract, Johnson signed with Singapore-based promotion
ONE Championship and faced former
UFC heavyweight champion Tim Sylvia at
ONE Fighting Championship: Rise to Power on May 31, 2013. The fight was contested at a catchweight of 271 lbs. after Sylvia missed weight. Johnson won the fight via TKO due to a doctor stoppage in the third round after an elbow by Johnson opened up a cut on Sylvia's forehead. Johnson next faced Chris Lokteff at
ONE Fighting Championship: Warrior Spirit on November 15, 2013. He lost the fight via split decision.
Independent promotions Over a year later, on November 22, 2014, Johnson faced Robert Neal at V3 Fights: Neal vs. Johnson and won via TKO due to elbows in the very first round.
Return to Bellator Johnson re-signed with
Bellator and faced former
Bellator heavyweight champion Alexander Volkov at
Bellator 136 on April 10, 2015. He won the fight via split decision. One judge scored the fight 29–28 for Volkov, while the other two judges scored it 29–28 to Johnson. Johnson faced former professional boxer
Raphael Butler at
Bellator 148 on January 29, 2016. Johnson utilised his wrestling to take Butler down and wear him down, before the referee stopped the bout in favour of Johnson, late in the third round due to punches (TKO). Johnson faced
Cheick Kongo at
Bellator 161 on September 16, 2016. He lost via majority decision. One judge had it 28–28 (even), while the other two judges scored the bout 29–28 in favor of Kongo.
Kickboxing debut Johnson made his professional kickboxing debut on April 7, 2017 at SUPERKOMBAT World Grand Prix I 2017 in
Bucharest,
Romania, being defeated by TKO (doctor stoppage) in round 1. If Johnson had won his bout against
Lukasz Krupadziorow, he would have face
Cătălin Moroșanu at SUPERKOMBAT World Grand Prix II 2017 in
Madrid, Spain.
Absolute Championship Akhmat He fought for the vacant
ACA Heavyweight Championship against
Daniel Omielańczuk at
ACA 114: Omielańczuk vs. Johnson. He won the fight by KO in the first round, becoming the first opponent to knock him out in 36 fights. Johnson defended his title on April 23, 2021 at
ACA 122 against Dmitry Poberezhets. He won the bout via TKO from ground and pound in the third round. Johnson defended his title against Mukhumat Vakhaev on November 18, 2021 at
ACA 132: Johnson vs. Vakhaev. He won the bout after dropping Vakhaev and then finishing him on the ground at the end of the first round. Johnson was scheduled to make his third title defense against Salimgerey Rasulov at
ACA 137 on March 6, 2022. After being unable to obtain a visa in time, Johnson was forced to pull out of the bout. Johnson was rescheduled against Salimgerey Rasulov for
ACA 138 on March 27, 2022. He lost the bout and title after being knocked out in the first round. Johnson faced
Evgeniy Goncharov on September 23, 2022 at
ACA 145. He lost the bout via knockout at the end of the first round. In the Quarter-final of the
2023 ACA Heavyweight Grand Prix Johnson faced Anton Vyazigin on June 2, 2023 at
ACA 158: Mokhnatkin vs Olenichev, losing the bout via unanimous decision. Johnson rebounded in a rematch against Denis Smoldarev on November 3, 2023 at
ACA 165: Dakaev vs. Batista, knocking Smoldarev out twenty one seconds into the bout. Johnson faced
Carlos Felipe on March 29, 2024 at
ACA 173: Frolov vs. Yankovsky, winning the bout via split decision. ==Personal life==