He began in hockey by managing the last Great Britain team to win a gold medal at the Winter Olympic Games, before moving to the international stage.

[3] Ahearne was part of the IIHF delegation who travelled to North America in 1947 to convince the CAHA and the Amateur Hockey Association of the United States (AHAUS) to resume being active members.

[4] He served as the CAHA's representative in Europe until 1952, and booked European tours and accommodations for the Canada men's national ice hockey team.

[3] The alternating terms as president and vice-president arose from the agreement where the CAHA and AHAUS rejoined the IIHF with the promise of rotating the top position between Europe and North America.

[11] During his time with the IIHF, Ahearne is credited with improving its finances, cooperating with the International Olympic Committee (IOC), and helping to develop and introduce hockey to new countries.

[4] He also transformed the Ice Hockey World Championships into a well-known annual tournament,[2] and implemented the splitting of the event into different tiers of competition.

[4] He introduced advertisements on the side boards of hockey rinks during the World Championships, and secured broadcasting rights for international matches.

The decision was later challenged by the Soviet Union, claiming that Canada would abuse the change at the upcoming 1970 World Ice Hockey Championships.

[2][4] This dispute led to the negotiation of the 1972 Summit Series, of which Ahearne was one of the four signatories who approved the event on 18 April 1972, along with Fred Page, Joe Kryczka, and Andrey Starovoytov.