A native of Owen Sound, Ontario, Day played 13 NHL seasons for the Toronto St. Pats, Toronto Maple Leafs and New York Americans, then coached the Maple Leafs to five Stanley Cup championships during the 1940s, including three in a row (1947-49).

Mostly a defenseman in his playing days, he had 207 points (86 goals, 121 assists) in 586 regular-season games. Day made his NHL debut Dec. 13, 1924, with the St. Pats and played that season as a left wing, scoring 27 points (10 goals, 17 assists) in 26 games. He shifted to defenseman the following season and stayed there for the remainder of his career.

Considered a natural leader, Day was named Maple Leafs captain in 1927 and held that role for 10 seasons. With defense partner King Clancy, Day helped them win the Stanley Cup in their first season at Maple Leaf Gardens (1931-32). Day had six points (three goals, three assists) in seven games that postseason.

Day played another five seasons in Toronto before finishing his playing career in New York, where he played the 1937-38 season and had three assists in 43 games.