Born to a Korean mother and American father, Johnny was a state wrestling champion at Park Hill High School in Kansas City. He wrestled collegiately at the University of Missouri, where he became a NCAA qualifier in 2015 and a two-time Academic All-MAC Team member, posting three 20-win campaigns and compiling an 87-24 career record.

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After relocating to Florida post-graduation in 2015, he was invited to visit American Top Team by former Olympic wrestler and ATT coach, Steve Mocco. Johnny started his professional MMA career two years later with Shamrock FC, making his debut at Shamrock FC 291 where he defeated Wayne Collier via TKO in the first round, igniting what would be his first of many victories as a pro-fighter.

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WIth his record standing at 4-0, Johnny transitioned to Bellator MMA in 2019 at Bellator 219. Three years and seven victories later, he faced Gegard Mousasi for the Bellator Middleweight Championship title at Bellator 282 and won via unanimous decision. He has successfully defended that title twice and was named #5 in Bellator's pound-for-pound rankings.

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Johnny currently still stands as the Bellator Middleweight Champion with a perfect 16-0 record.