Appearing in a single game with the Montreal Shamrocks of the Amateur Hockey Association of Canada in 1897, he secured a regular shift with the club the following year. 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. On February 4, 1899, Trihey amassed ten goals in one game in a match versus Quebec, which remains the record for the most goals scored by a single player in a major senior regular season match. He went on to score the only goal of the second to the last game of the regular season against the perennial champion Montreal Victorias, which clinched the regular season title for the Shamrocks and earned them the right to defend the Stanley Cup. The defence took place on March 14 against Queen's University of Ontario, a match won by the Shamrocks 6-2, led by Trihey's three goals. In the off-season, he also served on the athletic club's lacrosse side.