Early career Johnson made his amateur MMA debut in 2013, compiling an impressive 3–0 record as a
Heavyweight. He then turned professional in 2014, amassing an undefeated professional record of 6–0, while becoming the final RFA champion in the process. In January 2017, Johnson was signed by the
UFC.
Ultimate Fighting Championship Johnson made his promotional debut against
Henrique da Silva on January 28, 2017, at
UFC on Fox 23. He won the fight via unanimous decision. Johnson faced
Marcel Fortuna on July 7, 2017 at
The Ultimate Fighter 25 Finale. He won the fight by unanimous decision. Johnson faced
Adam Milstead on March 3, 2018 at
UFC 222. He won the fight by split decision. Johnson faced promotional newcomer Adam Yandiev, replacing injured
Krzysztof Jotko, on September 15, 2018 at
UFC Fight Night 136. He won the fight by submission in the second round. As Johnson didn't agree with the financial terms of UFC's contract extension offer after the fight with
Adam Milstead, he became a free agent after the fight with Yandiev.
Professional Fighters League On March 21, 2019, Johnson was revealed to be competing in the light heavyweight bracket of
Professional Fighters League's second season. He made his debut against
Maxim Grishin at
PFL 3 on June 6, 2019. He lost the fight by unanimous decision. Johnson was set to face
Tom Lawlor on April 29, 2021 at
PFL 2 as the start of the 2021 PFL Light Heavyweight tournament. However, in March, it was announced that Johnson pulled out and was replaced by
Antônio Carlos Júnior. Later, PFL announced that
Antônio Carlos Júnior will replace Johnson for the whole season. ==Mixed martial arts record==