Cameron was considered one of the best puck-rushing, offensive-minded defensemen of the early days of the NHL.

Cameron grew up in Pembroke, Ontario, where one of his closest friends and teammates was fellow Hockey Hall of Fame member Frank Nighbor, and they joined the Toronto Blueshirts of the National Hockey Association in 1912-13. Nighbor left after one season but Cameron blossomed in Toronto. He finished second in scoring among NHA defensemen twice in five seasons, including a high of 20 points (12 goals, eight assists) in 17 games in 1914-15. In 1913-14 he scored the winning goal in Game 3 of the Stanley Cup Final against the Victoria Aristocrats as Toronto swept the best-of-5 Final.

He remained with Toronto when it joined the NHL and became the Arenas in 1917-18, and in his first season in the new League he led NHL defensemen in goals (17), assists (10) and points (27). In the NHL playoffs he had three points (one goal, two assists) against Montreal during the two-game NHL championship series, which was decided on total goals. Then he had four points (three goals, one assist) against the Vancouver Millionaires to help Toronto win the Stanley Cup.

Cameron's best individual season was 1921-22 when his 35 points (18 goals, 17 assists) led NHL defensemen and was fourth among all players. He had four assists in six games when Toronto, now known as the St. Patricks, defeated Ottawa in the two-game, total-goal NHL final, and then helped the St. Patricks beat Vancouver in five games to win the Stanley Cup.

He led or tied for the lead among NHL defensemen in scoring in each of the League's first five seasons, topped by 35 points (18 goals, 17 assists) in 1921-22, a total no defenseman topped until King Clancy had 40 in 1929-30. Cameron's 18 goals in 1920-21 and 1921-22 were the most by an NHL defenseman until Baldy Northcott scored 19 in 1931-32, and are tied for the 12th highest in a season during the League's pre-expansion era (prior to 1966-67).

Cameron's final NHL season was 1922-23, when he had 16 points (nine goals, seven assists) in 23 games. In six seasons with Toronto, the Ottawa Senators and Montreal Canadiens he had 142 points (88 goals, 54 assists) in 129 games. He continued to play professionally until 1933, and was inducted into the Hockey Hall of Fame in 1962.