He served in World War I first as commanding officer of the newly raised militia unit, the 55th Regiment, The Irish Canadian Rangers, then overseas with the newly raised CEF battalion, the 199th Battalion Duchess of Connaught's Own Irish Rangers, CEF, and held the post of Port Commissioner for the Montreal Harbor Commission in later years.

[3] Teamed with linemates Arthur Farrell and Fred Scanlan in 1899, Trihey was named captain of the "Fighting Irish" and had a breakout season, leading the league in scoring with 19 goals.

[8] Already respected enough to serve on a competition committee regarding the adoption of goal nets[9] and to be quoted as the preeminent authority on forward play by his linemate Arthur Farrell in his 1899 book,[1] Trihey continued his high level of play in 1900, once again leading the Shamrocks to an easy league championship, while repeating his league scoring championship with 17 goals.

[16] He also served as a referee both for league and Stanley Cup play[17] and sat on the advisory board of the Montreal Wanderers Hockey Club.

[18][19][16] Trihey resigned his commission and returned to Montreal in 1917 after the British army reversed its earlier promise to send the Rangers into battle as a discrete unit, instead choosing to plug them into the front line as reinforcements, and in the wake of unrest over the Easter Rising in Ireland in 1916.

[20] Later in life, he was a partner in the law firm of Plimsoll and Coonan from the 1920s to 1932,[21] and served as a Port Commissioner of the Montreal Harbor Commission.