Harmon attended St Bede's College in Christchurch and during that time, he was selected as a member of the New Zealand Schools Barbarians squad for their matches against Australia and Samoa in 2012.
[2] After leaving school, Harmon played for New Brighton again in club rugby while working full-time as a plumber.
He was in excellent form during the 2016 club rugby season, captaining New Brighton to the final of the Hawkins Division 1 Trophy.
[3] His impressive club form didn't go unnoticed and through 2015 and 2016 he spent time with the Crusaders Academy and turned out for Canterbury's Colts and Maori sides.
[4] At the end of 2020, Harmon signed a two-year deal to play for the Highlanders in Super Rugby.