Mezue ahịrịokwu na-esonụ: Johnston mere ya mpụta mbụ maka Munster na 5 September 2015, na-amalite na mmeghe egwuregwu nke
2015<unk>16 Pro12 megide Benetton. Na Jenụwarị 2016, ekwuputara na Johnston bịanyere aka na nkwekọrịta ya na Munster nke ga-ahụ ka ọ sonye na ndị isi ndị isi site na oge 2016-17, nke mbụ na nkwekọrịta mmepe wee, site na 2017-18, na nkwekọrịta zuru ezu. A họpụtara Johnston maka Munster Academy Player nke Afọ 2016.