2008-09: Gallagher, a ninth round selection by the Vancouver Giants at the 2007 WHL Bantam Draft, played in 52 games for the Giants. He scored 10 goals and added 21 assists for 31 points while posting a +26 rating and 61 penalty minutes. In 16 playoff games for the Giants, he scored 1 goal and added 2 assists for 3 points.
2009-10: In 72 games for the Giants, Gallagher scored 41 goals and added 40 assists for 81 points, placing him 16th overall in WHL scoring. He racked up 111 penalty minutes on the season. In 16 playoff games for the Giants, Gallagher scored 11 goals and added 10 assists for 21 points.
2010-11: Gallagher was the leading scorer for the Vancouver Giants in his third WHL season as the Giants finished second in the British Columbia Division. Gallagher scored 44 goals with 47 assists and was a team-best +30 plus/minus. Gallagher's offensive numbers were matched by his physical play – his 108 PMs were second-most on the team behind defenseman Wesley Vannieuwenhuizen. The Giants proved no match for United States Division foe Tri-City in the WHL playoffs and Gallagher finished with 2 goals and 16 PMs with an even plus/minus in the four-game series.
2011-12: Gallagher had an outstanding year starting with the Canadiens' training camp, playing in NHL pre-season games and for Team Canada at the 2012 World Junior championship. The little ball of energy also signed an NHL entry level contract with the Canadiens and finished the season as the all-time franchise leader with the most goals and points in the Vancouver Giants history. He scored 41 goals (14 on the power play) along with 36 assists and a solid plus 19 rating in only 54 WHL games this year. Gallagher and his Vancouver team lost a hard fought, physical first round series 4-2, in the 2012 WHL playoffs against the Spokane Chiefs. The feisty Giants' captain battle all over the ice and around the Chiefs net but still lost the series despite scoring five goals along five assists and an even rating while taking 14 PIMs in six playoffs games.
Gallagher has an excellent work ethic, grit, really good hands and a very quick, accurate release on his shot. The small physical winger doesn't need a lot of time or space to strike offensively and will take advantage of the smallest of chances. Although he has improved on his skating speed and added more muscle mass, the undersized forward will still need to increase both in order to play his style of game in the dirty areas around the net at the professional level.
2011-12 was Gallagher's final season in the WHL as most likely he'll will be playing at the professional level for the Canadiens' organization in the AHL or NHL this coming season.