Johnson began boxing at a local club in his home town of Boston from an early age but moved to train at Terry Allen Unique ABC in Lincoln by the time he was 16.

[2] Qualifying through his grandparents, Johnson boxed for Scotland at the 2010 Commonwealth Games in Delhi, defeating Northern Ireland's Thomas McCarthy in the 81kg light heavyweight final to win the gold medal.

[5] On 4 December 2010, he made his professional debut at the Braehead Arena in Glasgow, stopping Phillip Townley in the second-round on on the undercard of Ricky Burns' world title defence against Andreas Evenson.

He managed to drop the champion in the second-round with a left hook but Beterbiev recovered quickly and knocked Johnson to the canvas in the fourth round with a big right hand, forcing the referee to stop the fight.

[12][13] In his next bout, Johnson defeated Sean Monaghan, who was ranked #13 by the WBC at light heavyweight, with a third round technical knockout at Turning Stone Resort Casino, Verona, New York, on 9 March 2019.