He served as chairman of the CAHA committee which proposed a new definition of amateur to eliminate what it called "shamateurism", in the wake of Canada's struggles in ice hockey at the 1936 Winter Olympics.

He negotiated a series of agreements to protect the CAHA's interests, and to develop relationships with all other areas of the world where hockey was played.

Duncan's reforms also returned the CAHA to affluence after four years of deficits during the Great Depression and increased player registrations in Canada.

[5] He supported updating the residency rules to prevent mass movement of hockey players about the country, instead of the CAHA blindly approving the transfers due to the economic situation caused by the Great Depression.

[6] Duncan assembled an amateur Ottawa All-stars team of players from the National Capital Region to play an exhibition series in Europe during December 1931 and January 1932.

[17] He sat on the CAHA's registration committee which oversaw player transfer requests and implemented new regulations to prevent regional shifts of talent.

[23] He later contested the eligibility of the Montreal Senior Hockey Group for the Allan Cup playoffs due to charges of professionalism in the league.

[24] The 1935 Allan Cup champions Halifax Wolverines were chosen to represent Canada in ice hockey at the 1936 Winter Olympics.

[27] Duncan served as chairman of the CAHA committee which proposed a new definition of amateur, in the wake of Canada's struggles at the Olympics and loss of the gold medal to the Great Britain men's national ice hockey team.

The Winnipeg Free Press reported that support for the reforms was strong, despite opposition by the "old guard" within the AAU of C. Duncan also proposed a resolution that the word "amateur" be dropped from the CAHA name.

[37] The Winnipeg Tribune reported that Duncan and the CAHA had already taken the first steps to separate in November 1936, since players in the ODHA and the Saskatchewan Amateur Hockey Association were not required to get a registration card from the AAU of C.[38] Duncan announced that the CAHA had reached an alliance with the South African Ice Hockey Federation on December 9, 1936.

The agreement meant that the CAHA now had formal relations with all areas where organized hockey was played, including previous alliances with the United States, Great Britain and Europe.

[39] On December 15, 1936, Duncan formally notified new AAU of C president Jack Hamilton in writing that the CAHA would terminate its articles of alliance effective January 15, 1937.

[42] He ruled all leagues within the QAHA ineligible for national playoffs, except for the Montreal Senior Group which pledged allegiance to the CAHA and the Allan Cup and then considered setting up a committee to govern hockey in Quebec.

[47] Duncan felt that these changes gave associations more power to govern their own affairs and paved the way for the CAHA to introduce its own legislation for the immediate reinstatement of professionals as amateurs, instead of a five-year waiting period.

[49] Duncan announced plans for an International Amateur Hockey League to begin in the 1937–38 season, composed of an interlocking schedule between the Montreal Senior Group and the EAHL.

Duncan stated the choice was made based on where the CAHA felt interest would be greatest and remained firm on the decision.

Duncan inquired directly with the Quebec Aces as the league champions and reached an agreement for the team to participate in the playoffs despite the protest.

[52] Duncan was re-elected president of the CAHA in April 1937 and received a vote of confidence in how he handled the Allan Cup playoffs.

The CAHA planned two annual European tours and gave the Allan Cup champions and finalists the first right of refusal to go to Europe.

Duncan and fellow CAHA executives signed an agreement with EAHL president Tommy Lockhart to govern the movement of players, limit the number of transfers to the United States, and protect rosters in Canada.

Duncan established a CAHA committee to govern hockey in Quebec and invited teams interested in competing for the national championships.

[65] He was a guest at the CAHA silver jubilee hosted at the Royal Alexandra Hotel in Winnipeg, where eleven of thirteen past presidents were in attendance.

[16] In October 1936, Duncan tested a change to avoid automatic offside infractions in a match between the hometown Ottawa Senators and the visiting Springfield Indians.

[74] In April 1937, he appointed NHL referee Clarence Campbell as the interpreter of the playing rules and a reference person for branches in the CAHA.

[78] Duncan and NHL rules committee chairman Frank Boucher introduced the centre red line to the ice hockey rink in the 1943–44 season, in an effort to open up the game by reducing the number of offside infractions and create excitement with quicker counter-attacks.

He was part of a delegation to confer with James Ralston, the Minister of National Defence of Canada to determine the role of the Interprovincial Rugby Football Union which Duncan represented.

[85] At the 1947 general meeting of the CAHA, Duncan was opposed to the increasing commercialization of junior ice hockey and direct sponsorship of teams by the NHL.

[87] Duncan proposed a major series for senior ice hockey in 1948, since he was concerned that certain teams would continue to dominate Allan Cup competition.

[93] In November 1962, Duncan welcomed the Soviet Union national ice hockey team to Canada on behalf of the CAHA.