The first formal organization of intercollegiate athletics in Canada took place in 1906 with the formation of the Canadian Intercollegiate Athletic Union. This organization had four active members: Ottawa College, Trinity College, McMaster College and the Royal Military College. As the years passed, the CIAU expanded until in 1954 the union had nineteen members.
In 1954, the administration of the CIAU was becoming somewhat unwieldy. There was a great variation in the standards of play between institutions, a different philosophy towards athletics between many members and difficulties in agreeing upon common standards of eligibility. It was also felt that the name Canadian Intercollegiate Athletic Union was not truly appropriate since intercollegiate athletic associations were also in existence in other parts of the country. In 1955, it was agreed by the member institutions that the CIAU (Central Division as it was then called) would reorganize in two sections to be known as the Ontario-Quebec Athletic Association (with nine members) and the Ottawa-St. Lawrence Intercollegiate Association (with ten members).
The original members of the O-QAA had been joined by the Assumption College (University of Windsor) and were joined in 1961 by Waterloo and 1968 by Carleton University and the University of Ottawa. In 1968, the O-QAA was divided into Eastern and Western Divisions in order to facilitate the scheduling of events.
In 1971, the Quebec-based universities in the O-QAA withdrew from the Association. Laval, McGill and Montreal elected to pursue their future athletic endeavours in the newly formed Quebec Universities Athletic Association.
In the resulting reorganization meetings, the remaining members of the O-QAA, (Carleton University, University of Guelph, McMaster University, University of Ottawa, Queen's University, University of Toronto, University of Waterloo, University of Western Ontario and University of Windsor) voted to change their name to the OUAA (Ontario Universities Athletic Association). Invitations were extended to all Ontario universities to participate in the reorganization meeting.
As part of the reorganization, it was decided that all the trophies, records, etc. of the O-QAA would remain with and be recognized by the OUAA.
The Ontario Women's Interuniversity Athletic Association was founded in 1971, which provided athletic competition for women students in the universities of Ontario. The OWIAA was unique in North America in both its longevity and singleness of purpose. Formed by the amalgamation of the Women's Intercollegiate Athletic Union (WIAU), which was founded in 1923 and the Ontario-Quebec Women's Conference of Intercollegiate Athletics (O-QWCIA), the OWIAA continued the heritage of 50 years of women's interuniversity competition. This coalition was the only association for women's athletics to have survived through 60 years of commitment to women athletes in Ontario universities.
In the spring of 1972, the following institutions were admitted as full members of the OUAA: Brock University, Laurentian University, Ryerson Polytechnical Institute, Trent University, Waterloo Lutheran University and York University.
The Royal Military College of Kingston was admitted to the OUAA in 1973. Also in 1973, Waterloo Lutheran University changed its name to Wilfrid Laurier University. The continuing evolution of the OUAA saw three Quebec-based universities (Bishop's, Loyola (now Concordia) and McGill) receive "playing privileges" in the OUAA football league in 1974.
In 1980, football was reorganized so that the teams of the Ontario-Quebec Intercollegiate Football Conference- West Division would form the new OUAA Football League. The OQIFC East teams: Ottawa, Carleton and Queen's would join the three Quebec schools in the new OQIFC.
In 1987, the OUAA awarded playing privileges in hockey to three Quebec schools, McGill, Concordia and Trois Rivieres.
In 1988, Lakehead University was admitted to full membership while McGill, Concordia and Bishop's were granted playing privileges in basketball due to the folding of the Quebec Universities Athletic Association.
Nipissing University was admitted in 1993 with full membership.
July 1, 1997 marked a new era of university sport in Ontario. Both the OUAA and the OWIAA amalgamated to form one association, Ontario University Athletics. In November, 1997 the OUA hired the organization’s first Executive Director. The “new” OUA office opened on September 1, 1998 in Hamilton.
In 2001, the Queen’s Golden Gaels and the Ottawa Gee Gees football teams rejoined the OUA from the OQIFC, expanding the OUA Football Conference to ten teams.
The 2004-05 season saw Royal Military College enter completely into the OUA. In the past, the Kingston school had competed in both the OUA and OCAA, but withdrew from OCAA competition entirely.
In January of 2006, the OUA welcomed its 19th member to the fold as the University of Ontario Institute of Technology was granted membership in a unanimous vote by the league's Board of Directors. The Oshawa-based school began competition in the 2006-07 season, particpating in rowing and tennis, while joining men's and women's hockey in 2007-08.