Dhameystir weedha soo socota: Inta lagu guda jiro ciyaaraha 2010 ee ciyaaraha, Gallagher waxaa loo doortay inuu yahay Ciyaaryahanka Ragga ee Sannadka ee magaaladiisa Delta, British Columbia. Ka hor inta aan
2010 NHL Entry Draft, waxaa lagu qiimeeyay 152-aad oo ka mid ah ciyaartooyda Waqooyiga Ameerika ee u qalma in ay doortaan NHL Central Scouting Bureau. Gallagher waxaa doortay Montreal Canadiens markii 147-aad. Markii uu ku soo laabtay heerka hoose ka dib xeradii tababarka ee ugu horreysay ee uu la qaatay Canadiens, wuxuu diiwaan geliyay WHL xirfadiisa ugu sarreysa sanadka 2010<unk>11. Bishii Febraayo 28, 2011, waxaa loo magacaabay Ciyaaryahanka Toddobaadka ee WHL ka dib markii uu duubay toban dhibcood (shan gool iyo shan caawin) saddex kulan. Bishii Maarso 2011, Gallagher waxaa laga saaray ciyaarta dhaawac madaxa ah, ka dib markii uu dhaawac ka soo gaaray ciyaar ka dhan ah Portland Winterhawks. Isagoo kaalinta koowaad ka galay kooxda Giants iyo kaalinta siddeedaad ee dhamaan gool dhalinta WHL oo leh 91 dhibcood 66 kulan, waxaa loogu magac daray WHL West First All-Star Team. 44 gool oo uu dhaliyay ayaa kaliya afar ka gaabisay rikoodhkii kooxda ee Evander Kane ee hal xilli ciyaareed.