 Nyorai kuenderera mberi kweiyi ndima - Mumwaka wake wechitatu weWHL, Gallagher akakokwa kumusasa weWorld Junior weCanada junior timu muna Zvita 2010. Akakundikana kupinda muchikwata, akanga ari pakati pevakanga vatanga kuiswa. Gore rakatevera, Gallagher akaita chikwata che2012 World Junior Championships, rakaitirwa muAlberta. Mumakwikwi ekupedzisira emutambo wekutanga, Gallagher akatumidzwa zita reCanada mutambi wemutambo mushure mekurekodha mutambo wepamusoro-soro zvinomwe zvinopfura pachinangwa mukukunda 32 kurwisa United States. Mumakwikwi ekupedzisira, Gallagher akarekodha chinangwa uye zviviri zvinobatsira pazvinangwa zvitatu zvekupedzisira zveCanada, achivabatsira kuti vawane chinangwa chimwe chete chekudzima 61 kushomeka neRussia. Canada yakaenderera mberi kuhwina mutambo wavo wemenduru yebronze vachipesana neFinland 40. Gallagher akapedza mutambo uyu aine mapoinzi matanhatu zvinangwa zvitatu uye zvinobatsira zvitatu, achibatanidza nzvimbo yechishanu mukukwikwidza kwechikwata, uku achitungamira Canada nemapfuti makumi matatu nemashanu pachinangwa. Gallagher aivewo chikamu cheChikwata cheCanada mu2016 IIHF World Championship. Munguva yemutambo, akarova zvibodzwa zviviri uye zvibodzwa zvitatu zvehuwandu hwemapoinzi mashanu mumitambo gumi sezvo Canada yakahwina goridhe. 