Johnson came through the Great Britain Futures squad in 2011, earning himself a promotion onto the senior roster for EuroBasket in Lithuania, and then retaining his place for the 2012 Olympic Games. Johnson capped his college career by helping Brooklyn-based Long Island University capture the 2011 Northeast Conference Championship. He made his professional debut with Ilissiakos in Greece in 2011 before transferring to Apoel Nicosia. He spent the 2012-13 campaign in Italian Lega Basket with Sutor Montegranaro, as the club finished in 13th place. Born and raised in Canada, Johnson qualifies to play for Great Britain through his father Les. He names his mother Paulette as his greatest influence. He majored in business management at college.