Pedzisa mutsara unotevera: Johnston akaita kutanga kwake kweMunster musi wa 5 Gunyana 2015, achitanga mumutambo wokutanga we
2015<unk>16 Pro12 vachipesana naBenetton. Muna Ndira 2016, zvakaziviswa kuti Johnston akanga asaina chibvumirano neMunster iyo ichamuona achibatana nechikwata chevakuru kubva mumwaka wa 2016-17, kutanga pachibvumirano chekuvandudza uyezve, kubva muna 2017-18, pachibvumirano chakazara. Johnston akasarudzwa nokuda kwe2016 Munster Academy Player of the Year Award.