A professional lacrosse player with the Toronto Tecumsehs, Ion signed with the Vancouver lacrosse team in 1910. The team was run by hockey entrepreneurs Lester Patrick and Frank Patrick, and when they started the Pacific Coast Hockey Association in 1911, they hired several of their lacrosse players -- Ion among them -- to referee the league's games.
Ion quickly became the league's chief referee. Among his innovations was the first known season-ending All-Star team, the naming of which was a regular practice of his from then on and which received much publicity each year. His first such selection, in the 1913–14 PCHA season, had Hugh Lehman of New Westminster in goal, Ernie Johnson of New Westminster and Frank Patrick of Vancouver on defence, Cyclone Taylor of Vancouver as the rover, and Tom Dunderdale of Victoria, Eddie Oatman of New Westminster and Dubbie Kerr of Victoria at forward. He was well-known as being an iron man, officiating as many as four or five games in a week throughout western Canada.
Ion joined the Western Canada Hockey League as senior official when the PCHA folded in 1924, and the National Hockey League in 1926 when the western loop folded as well. He was later named referee-in-chief of the NHL, a position he held until 1942.
He was elected to the Hockey Hall of Fame - one of the first three referees to be so honoured - in 1961.