The year 1970 was pivotal for the slow evolving history of environmental regulation in Ontario. That was when a group of environmental activists and law professors, young lawyers and articling students gathered in an unused laboratory on the campus of the University of Toronto to form the Environmental Law Association (the "Canadian" would be added a few years later). The goal was to create a a public interest law clinic that could handle the heavy legal slogging for the newly-emerging environmental activists and groups fighting to control the most egregious polluters, safeguard air and water quality, and preserve natural areas.

[We had the idea that we] could use environmental laws to prevent pollution, to improve society and, to the extent that we had any environmental laws in those days, to try to enforce them.

In those early, formative days of environmental law, long before provincial and federal governments would vow to get tough on polluters, CELA undertook the first prosecutions for noise pollution in Ontario, pushed for public consultation on the first certificates of approval, and rallied support for broader, more inclusive environmental legislation. CELA also attracted a roster of prominent lawyers from private practice, including a future member of the Supreme Court, who would volunteer to argue groundbreaking cases. Over the years, CELA has been instrumental in the development and passage of Ontario's Environmental Assessment Act, the Safe Drinking Water Act, and the Environmental Bill of Rights. The association was also known for fighting and (mostly) winning a series of precedent-setting court cases. CELA lawyers

• defended the Hudson, Quebec, municipal bylaw outlawing the use of cosmetic pesticides on private property
• won a ruling in the Supreme Court that higher life forms cannot be patented in Canada
• opposed both the proposed Adams Mine mega-dump and plans by Lafarge Canada to burn tires and other waste in an Ontario cement plant.

Following several precarious years of unpredictable and unstable funding in the early 1970s – where the organization's limited financial backing was supplemented by personal loan guarantees assumed by several of CELA's directors and individual supporters – the association was finally recognized by Legal Aid Ontario as a specialty community legal clinic. This allowed the organization to hire support staff, move into more permanent offices, and retain some of the expert counsel and researchers it had been training over the years. From the beginning, CELA helped establish the discipline of environmental law and their influence is visible even today. They established a Resource Library for the Environment and the Law, provided a hands-on training ground for hundreds of articling students, researchers, staff lawyers and directors who have gone on to play influential roles in the public and private sector, and produced resources and materials that environmental lawyers continue to rely on. The Canadian Environmental Law Reports, now circulated by Carswell, is still the country's primary environmental law reporting service, while 1974's encyclopedic Environment on Trial became the de facto textbook for the new courses in environmental law that started to appear law school calendars across the country. CELA  established the Canadian Environmental Law Research Foundation (CELRF), which was able to obtain federal charitable status and could raise funds to support the legal clinic, while also undertaking arm's-length law reform projects and research grants. CELRF later evolved into the Canadian Institute of Environmental Law and Policy (CIELAP). CELA also launched the first Canadian Environmental Defence Fund (now called Environmental Defence Canada).