Rubuta ci gaba don wannan sakin layi - A lokacin wasan karshe na 2010, an zabi Gallagher a matsayin Dan wasan Matasa na Shekara a garinsu na Delta, British Columbia. A cikin tsammanin 2010 NHL Entry Draft
, ya kasance na 152 a cikin 'yan wasan Arewacin Amurka da suka cancanci zaɓa ta Hukumar Kula da Scout ta NHL. Gallagher ya zaba 147th gaba ɗaya ta Montreal Canadiens. Komawa zuwa ƙarami bayan sansanin horo na farko tare da Canadiens, ya yi rikodin WHL mafi girma a cikin 2010<unk>11. A ranar 28 ga Fabrairu, 2011, an kira shi WHL Player na mako bayan ya yi rikodin maki goma (gobi biyar da taimako biyar) a wasanni uku. A watan Maris na 2011, Gallagher ya kasance tare da raunin kai, wanda ya ci gaba bayan ya sami nasara a wasan da Portland Winterhawks. Matsayi na farko a kan Giants da na takwas a cikin dukkan masu zira kwallaye na WHL tare da maki 91 a cikin wasanni 66, an sanya shi a cikin WHL West First All-Star Team. Kwallaye 44 da ya ci sun kasance 'yan kunya hudu ne kawai na Evander Kane na rikodin ƙungiyar guda ɗaya.